The effect of tin on the toughness of some common steels
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EXPERIMENTAL T I N is a p o t e n t i a l o b s t a c l e to the r e c y c l i n g of the m a g n e t i c f r a c t i o n of m u n i c i p a l s o l i d s w a s t e s . One r e a s o n a b l e s c e n a r i o ' f o r e c a s t s an a v e r a g e r e s i d u a l t i n l e v e l of about 0.016 pct in A m e r i c a n s t e e l by 1985, w h e r e a s the c u r r e n t l e v e l is about 0.008 pct. The tin l e v e l in a s m a l l p e r c e n t a g e of the s t e e l heats will, of c o u r s e , s u b s t a n t i a l l y exceed the f o r e c a s t e d a v e r a g e . V a r i o u s s t r a t a g e m s for coping with this p r o b l e m have b e e n suggestedJ M a x i m i z i n g the sound use of s c r a p that c o n t a i n s tin w i l l r e q u i r e m o r e e x t e n s i v e q u a n t i t a t i v e knowledge about the effect of t i n on the p r o p e r t i e s of v a r i o u s g r a d e s of s t e e l . Although a n u m b e r of i n v e s t i g a t o r s have studied the effect of tin on the t e n s i l e p r o p e r t i e s of v a r i o u s s t e e l s , only a few have r e p o r t e d on the effect of t i n on i m p a c t t o u g h n e s s . 2 In g e n e r a l , i n v e s t i g a t o r s have found that tin i n c r e a s e s s t r e n g t h , d e c r e a s e s d u c t i l i t y , and, to a g r e a t e r or l e s s e r d e g r e e , d e c r e a s e s impact toughness. T i n is a s t r o n g e m b r i t t l i n g agent in the t e m p e r e m b r i t t l e m e n t of quenched and t e m p e r e d a l l o y s t e e l s , 3 in which case it s e g r e g a t e s to p r i o r a u s t e n i t e g r a i n b o u n d a r i e s and p r o m o t e s i n t e r g r a n u l a r failure.4-7 A l though t e m p e r e m b r i t t l e m e n t is l e s s m a r k e d in p l a i n c a r b o n s t e e l s , 3 t i n has b e e n shown to s e g r e g a t e to f e r r i t i c g r a i n b o u n d a r i e s of i r o n s as well as to i n c r e a s e t r a n s i t i o n t e m p e r a t u r e and i n t e r g r a n u l a r f a i i u r e of a i r and f u r n a c e cooled F e - C alloys and one p l a i n c a r bon s t e e l . %~~ C o n s e q u e n t l y , one might expect t i n to d e c r e a s e the t o u g h n e s s of c o m m o n c a r b o n and low alloy s t e e l s . However, at the p r e s e n t state of knowledge, the magnitude of that e m b r i t t l e m e n t can be d e t e r m i n e d only by e x p e r i m e n t . The p r i m a r y p u r p o s e of this i n v e s t i g a t i o n was to b e t t e r define the effect of tin on the Charpy t o u g h n e s s of plate, s t r u c t u r a l , Iinepipe, and r a i l s t e e l s in s e v e r a l heat t r e a t e d c o n d i t i o n s . To put the c h a n g e s i n toughn e s s into b e t t e r p e r s p e c t i v e , the effect of tin on t e n s i l e p r o p e r t i e s was a l s o studied. F i n a l l y , in a n a t t e m p t to identify the e m b r i t t l i n g m e c h a n i s m , s o m e s p e c i m e n s w e r e e x a m i n e d by s c a n n i n g e l e c t r o n m i croscopy. E. T. STEPHENSON is Semo
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