Electrode polarization in the DC electroslag melting of pure iron
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CaO) + C = CO(g) + C a ( g ) A t v e r y h i g h c u r r e n t d e n s i t i e s b o t h the a n o d i c a n d c a t h o d i c p r o c e s s e s m a y c o n v e r t t o a r c s , l e a d i n g t o p r o c e s s i n s t a b i l i t y . T h e c h e m i c a l a n d t h e r m a l e f f e c t s of t h e o v e r p o t e n t i a l s a r e b r i e f l y d i s c u s s e d a n d c o m p a r e d w i t h the p r e s e n t r e s u l t s on ESR i n g o t s o f p u r e i r o n .
T H E e l e c t r o s l a g m e l t i n g p r o c e s s is p r e s e n t l y o p e r a t e d p r e d o m i n a n t l y on l i n e - f r e q u e n c y s i n g l e - p h a s e a c power, although s e v e r a l p l a n t s use d i r e c t c u r r e n t . H o w e v e r , f o r r e a s o n s p r i m a r i l y o f i n d u c t i v e l o s s e s in t h e l e a d s , f u r n a c e s m a k i n g i n g o t s i n the >200t r a n g e u s e e i t h e r 25 H z f r e q u e n c y c u r r e n t , o r a r e p r o j e c t e d to use d i r e c t c u r r e n t . The e l e c t r o s l a g w e l d i n g p r o c e s s i s u s e d w i t h both d i r e c t a n d a l t e r n a t i n g c u r r e n t . I n t h e c a s e of dc i n g o t - m a k i n g p r o c e s s e s , m o s t f u r n a c e s h a v e been constructed following v a c u u m arc practice with t h e c o n s u m a b l e e l e c t r o d e a s the n e g a t i v e p o l e . T h e i n g o t a n d m o l d a r e then a t the s a m e p o t e n t i a l , w h i c h i s n o r m a l l y g r o u n d p o t e n t i a l . The c u r r e n t f l o w in such a d e s i g n h a s b e e n p r e v i o u s l y d i s c u s s e d .1 D i f f e r e n c e s in ingot oxygen a n d s u l f u r c o n t e n t s have been found dep e n d i n g on w h e t h e r the i n g o t h a s b e e n m a d e w i t h the e l e c t r o d e p o s i t i v e o r n e g a t i v e , o r by u s i n g a l t e r n a t i n g c u r r e n t . 2'3 H o w e v e r , s i n c e d i f f e r e n c e s i n s p e c i f i c m e l t - r a t e ( k w - h r p e r ton) h a v e a l s o b e e n n o t e d , % 5 i t i s a s y e t u n c l e a r w h e t h e r s u c h c h a n g e s a r e the r e s u l t of r e a l c h e m i c a l r e a c t i o n c h a n g e s , o r of m e t a l r e s i d e n c e t i m e i n the r e a c t i o n z o n e s • A p r o c e s s p a t e n t e x i s t s8 i n w h i c h a dc p o t e n t i a l , s u p e r i m p o s e d on a n a c e l e c t r o s l a g p r o c e s s , by m e a n s of a u x i l l i a r y g r a p h i t e e l e c t r o d e s , is held t o a c c o m p l i s h e l e c t r o l y t i c c o m p o s i t i o n changes• In a dc o r a c p r o c e s s , i n t h e a b s e n c e o f a n a r c , the c u r r e n t m u s t p a s s a c r o s s the m e t a l / s l a g i n t e r f a c e by A. MITCHELL and G. BEYNON are Associate Professor and Graduate Student, respectively,Metallurgy Department, University of British Columbia, Vancouver, British Columbia, Canada. Manuscript submitted February 8 , 1971. METALLURGICAL
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