Homogenization of sulfide inclusions in low alloy steel
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i n F i g . 4 . T h e s u l f i d e s t e n d t o be g e n e r a l l y l a r g e r , a s n o t e d by c o m p a r i n g F i g s . 2 a n d 4 . A l s o , t h e d i m ples a r o u n d t h e m a j o r inclusions, i.e., t h e a r e a s bet w e e n m a j o r i n c l u s i o n s , a r e m u c h s m o o t h e r in t h i s m a t e r i a l . T h i s is i n d i c a t e d in Fig. 4 w h e n c o m p a r e d
ALEXANDER D. WILSON A r e c e n t s e r i e s of p a p e r s by K a t t a m i s , M e h r a b i a n a n d c o w o r k e r s 1-3 h a s i d e n t i f i e d s p e c i f i c s t a g e s i n t h e h o m o g e n i z a t i o n o f m a n g a n e s e sulfide i n c l u s i o n s in l o w alloy s t e e l s u s i n g quantitative light metallographic t e c h n i q u e s . T h e i r i n v e s t i g a t i o n s s h o w e d that t h e f l a t t e n e d a n d e l o n g a t e d M n S i n c l u s i o n s in a r o l l e d s t e e l f i r s t " c y l i n d e r i z e " upon heat t r e a t m e n t at 1583 K . A t l a t e r s t a g e s t h e s e c y l i n d e r s b r e a k up into segments, w h i c h spheroidize and then c o a r s e n and d e c r e a s e in n u m b e r . Our s t u d i e s h a v e c o n t r i b u t e d t o the f u r t h e r u n d e r s t a n d i n g o f t h e s e s t a g e s i n s u l f i d e h o m o g e n i z a t i o n , t h r o u g h f r a c t o g r a p h i c s t u d i e s of Charpy V n o t c h (CVN) impact specimen f r a c t u r e s . T h i s i n v e s t i g a t i o n was c o n c e r n e d w i t h a n A S T M A533 G r a d e B C l a s s 1 l o w a l l o y s t e e l p l a t e , w h i c h h a d b e e n c o n v e n t i o n a l l y p r o c e s s e d in t h e m i l l a n d was in t h e q u e n c h e d , t e m p e r e d a n d s t r e s s - r e l i e v e d c o n d i t i o n . T h e c h e m i c a l analysis o f t h i s m a t e r i a l is g i v e n i n T a b l e I . T h e e x a m i n a t i o n of t h r o u g h - t h i c k n e s s CVN i m p a c t f r a c t u r e s f r o m t h e a s - p r o c e s s e d m a t e r i a l in t h e S c a n n i n g E l e c t r o n M i c r o s c o p e ( S E M ) r e v e a l e d that T y p e II M n S inclusions were p r o m i n e n t . Fig. 1 e x h i b i t s t h e s e T y p e I I sulfide f o r m a t i o n s . T h e elongated and pancaked n a t u r e of most of t h e s e inc l u s i o n s is e v i d e n t . H o w e v e r , s o m e i n c l u s i o n s a p p e a r cylindrical, while o t h e r s indicate that t h e s e cylind e r s a r e b r e a k i n g up a n d s t i l l o t h e r a r e a s h a v e p a t c h e s o f r o u n d e d sulfides. T h e cylinders t h a t are p i n c h i n g off h a v e a d u m b b e l l s h a p e a n d a r e s p e c i f i cally i n d i c a t e d in Fig. 1. T h i s i n d i c a t e s t h a t in a n y o n e a r e a o f t h i s m a t e r i a l t h e v a r i o u s s t a g e s of h o m o g e n i z a t i o n h a v e b e e n e x p e r i e n c e d by t h e M n S i n c l u s i o n s . T h i s h a s m o s t l i k e l y h a p p e n e d a s a r e s u l t of t h e h e a t i n g p r i o r t o r o l l i n g of
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