The effect of composition on the resistivity of carbon steel sheet
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e l e c t r i c a l r e s i s t i v i t y o f c a r b o n s t e e l is o f i m p o r t a n c e , f o r e x a m p l e , in t h e d e s i g n o f e l e c t r i c a l m a c h i n e r y a n d in t h e d e s i g n o f c a t h o d i c p r o t e c t i o n s y s t e m s . Previous investigations have s h o w n the eff e c t s of s e v e r a l e l e m e n t s o n t h e r e s i s t i v i t y of e l e c t r i c a l steels,1 line-pipe steels,2 a n d b i n a r y a l l o y s o f i r o n . a I n the p r e s e n t i n v e s t i g a t i o n , it i s s h o w n that t h e resistivities of low-carbon f e r r i t i c s t e e l s h e e t s a r e c o r r e l a t e d w i t h M n , P , S, Si, C u , N i , a n d C r c o n t e n t s by a l i n e a r a d d i t i v e r u l e ( M a t t h i e s s e n ' s r u l e ) a n d that t h e c o e f f i c i e n t s o b t a i n e d a r e v e r y c l o s e to t h o s e obtained for pure b i n a r y alloys. A 3 2 - h e a t s e r i e s o f e x p e r i m e n t a l s t e e l s was dei s i g n e d a n d m e l t e d . T h e d e s i g n c o n s i s t e d o f a ~- r e p l i c a t e o f s e v e n e l e m e n t s - - M n , P , S, Si, C u , N i , a n d Cr, each at two levels. T h i s d e s i g n p e r m i t t e d t h e a s s e s s m e n t o f all main e f f e c t s with f r e e d o m f r o m interdependence a m o n g the independent v a r i a b l e s . Each heat was m e l t e d in a 5 0 - l b . v a c u u m - i n d u c t i o n f u r n a c e a n d c a s t into a s l a b m o l d . T h e r e s u l t i n g i n g o t s w e r e c o n d i t i o n e d , hot r o l l e d , p i c k l e d , a n d c o l d r o l l e d t o 0 . 0 3 0 i n . - t h i c k s t r i p . A s a m p l e o f s t r i p f r o m e a c h s t e e l was b o x - a n n e a l e d f o r 14 h r a t 1 3 0 0 ° F . T h e c h e m i c a l a n a l -
y s e s of t h e r e s u l t i n g p r o d u c t a r e g i v e n i n T a b l e I . Duplicate s p e c i m e n s with dimensions s h e e t thickn e s s by 0.25 i n . by 4.12 i n . w e r e s h e a r e d f r o m a n a n n e a l e d s a m p l e of each s t e e l with long axes (current d i r e c t i o n ) p a r a l l e l , p e r p e n d i c u l a r , a n d at 4 5 d e g to t h e roiling direction. T h e c r o s s - s e c t i o n a l a r e a , A , of each specimen was computed from its m a s s , M , length, L, and a common density 7.871 g per cu cm: A = 3 4 / ( 7 . 8 7 1 "L). I r o n potential l e a d s were s p o t w e l d e d t o e a c h s a m p l e a n d t h e s e p a r a t i o n was m e a s u r e d with a traveling microscope. E i g h t s a m p l e s were m e a s u r e d s i m u l t a n e o u s l y in a t e m p e r a t u r e - c o n t r o l l e d c h a m b e r ( 2 6 . 7 5 ° ± 0 . 1 5 ° C ) by a f o u r - p r o b e t e c h n i q u e . E r r o r s in t h e r e s i s t i v i t y d e t e r m i n a t i o n s a r e e s t i m a t e d t o be a b o u t 0 . 0 1 m i c r o h m - c m a n d 0 . 0 0 6 m i c r o h m - c m due t o u n c e r t a i n t i e s i n t e m p e r a t u r e a n d lead separation, r
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