Optimizing fracture toughness and abrasion resistance in white cast irons

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H I G H C r - M o white c a s t i r o n s a r e w e l l known fo r t h e i r good a b r a s i o n r e s i s t a n c e . 1 A b r a s i o n is a type of w e a r that o c c u r s under the r e l a t i v e m o v e m e n t of a hard body, e . g . m i n e r a l o r w o r k - h a r d e n d w e a r p a r t i c l e , and the s o f t e r s u r f a c e of a m a t e r i a l . In the a b r a s i v e p r o c e s s , the hard body may be f r a c t u r e d and the s o f t e r s u r f a c e w i l l be c r a c k e d a n d / o r d e f o r m e d , and m a t e r i a l will be r e m o v e d f r o m the s u r face, r e s u l t i n g in a m e a s u r a b l e v o l u m e l o s s . Mining and e a r t h m o v i n g e q u i p m e n t m u s t w i th s ta n d s e v e r e s e r v i c e s t r e s s e s and loading r a t e s , t h e r e f o r e , i n d u s t r i a l a p p t i c a t i o n s of white c a s t i r o n s u n d e r a b r a s i v e c o n d i t i o n s a r e f r e q u e n t l y l i m i t e d by t h e i r t o u g h ness. G e n e r a l l y , a b r a s i o n r e s i s t a n c e i n c r e a s e s , as a f i r s t a p p r o x i m a t i o n with i n c r e a s i n g m a t e r i a l h a r d n e s s , 2 while f r a c t u r e t o u g h n e s s g e n e r a l l y d e c r e a s e s with i n c r e a s i n g h a r d n e s s o r s t r e n g t h . 3'4 T h e r e f o r e , an o p p o s i t e e f f e c t of h a r d n e s s on the two p r o p e r t i e s m u s t be e x p e c t e d . In addition to h a r d n e s s , a b r a s i o n r e s i s t a n c e is i n f l u e n c e d by m i c r o s t r u c t u r a l p a r a m e t e r s s u c h as quantity of c a r b i d e s , c a r b i d e m o r p h o l o g y , r e t a i n e d a u s t e n i t e , i n t e r n a l n o t c h e s and the s t r u c t u r e of the m a t r i x , v'8 T h e s e f a c t o r s a l s o in f lu e n c e f r a c t u r e t o u g h n e s s . %~ T h i s i n f l u e n c e has a l s o b e e n found in s t e e l s and g r a y or d u c t i l e i r o n s . While f r a c t u r e t o u g h n e s s , under the condition of l i n e a r f r a c t u r e m e c h a n i c s , is an i n t r i n s i c p r o p e r t y of a m a t e r i a l o r of a m i c r o s t r u c t u r e , a b r a s i o n r e s i s ta nc e is r a t h e r an e x t r i n s i c p r o p e r t y . W e a r l o s s due to a b r a s i o n d ep en d s s t r o n g l y on the w e a r s y s t e m . 9 High C r - M o white c a s t i r o n s c o n s i s t of a c o m p o s i t e of l a r g e p r i m a r y a n d / o r e u t e c t i c c a r b i d e s ( m a s s i v e KARL-HEINZ ZUM GAHR, formerly Visiting Research Metallurgist, Chmax Molybdenum Co. Research Laboratory, is now Senior Engineer, Instatut fflr Werkstoffe, Ruhr-Universatht Bochum, Bochum, West Germany, and DOUGLAS V. DOANE is Associate Director of Research, Climax Molybdenum Company of Michigan, a subsidiary of AMAX Inc., Ann Arbor, MI 48106. Manuscript submitted July 9, 1979. METALLURGICAL TRANSACTIONS A

c a r b i d e s ) of the type MTCa in a s o f t e r m a t r i x . T he m a t r i x s t r u c t u r e f

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