Phase equilibria in the iron-molybdenum-1 Pct carbon system between 1143 and 1253 K
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T H E p u r p o s e of this i n v e s t i g a t i o n was to r e e x a m i n e the i r o n - r i c h , 1 p c t c a r b o n p o r t i o n of the 1143 K (1600~ 1198 K (1700~ and 1253 K (1800~ i s o t h e r m a l s e c t i o n s of the F e - M o - C s y s t e m in view of the l i m i t e d i n v e s t i g a t i o n s of the F e - M o - C s y s t e m at t h e s e t e m p e r a t u r e s and the i m p o r t a n c e of t h e s e t e m p e r a t u r e r a n g e s f o r h o m o g e n i z a t i o n , a n n e a l i n g , and heat t r e a t ment f o r c o m m e r c i a l a l l o y s . P a r t i c u l a r a t t e n t i o n was given to the i d e n t i f i c a t i o n of s t a b l e c a r b i d e s and the a u s t e n i t e s o l v u s at t h e s e t e m p e r a t u r e s . F e - M o - 1 pet C a l l o y s containing up to 5 pet Mo w e r e e x a m i n e d . The l a t t e r c o m p o s i t i o n r a n g e b r a c k e t s the l e v e l s of m o l y b d e n u m g e n e r a l l y found in tool and w e a r r e s i s t a n t s t e e l s , and 1 pet C is a t y p i c a l c a r b o n content of t h e s e s p e c i a l p u r p o s e a l l o y s . T h i s w o r k c o m p l e m e n t s our e a r l i e r p u b l i s h e d w o r k on the F e - C r - C s y s t e m at 1143 K. ~ In the p r e s e n t study, i n f o r m a t i o n about the s t r u c t u r e , quantity and c o m p o s i t i o n s of the p h a s e s p r e s e n t in the r a n g e of a l l o y s t e s t e d was obtained by e l e c t r o n m i c r o p r o b e a n a l y s i s , s e l e c t i v e etching, and X-ray diffraction studies. The F e - M o - C s y s t e m has been i n v e s t i g a t e d m a n y t i m e s o v e r the p a s t 25 y e a r s . H o w e v e r , m o s t of the w o r k has b e e n at t e m p e r a t u r e s of 973 K and l o w e r 2-6 o r 1273 K o r h i g h e r , v-x~ Two e x c e p t i o n s w e r e the w o r k of C a m p b e l l e t al, ~ who i n v e s t i g a t e d the s y s t e m at t e m p e r a t u r e s of 998 to 1588 K (1340 to 2400~ and Sato e l al, ~2 who s t u d i e d the c a r b i d e s p r e s e n t in 22 a l l o y s that had b e e n a n n e a l e d f o r 5 o r 50 h at 1173 K (1650~ In his r e v i e w of the s y s t e m , Wada ~3 included both v e r t i c a l s e c t i o n s of the d i a g r a m f r o m 873 to 1873 K (1110 to 2910~ for 2, 4, 10, and 20 pet m o l y b d e n u m and i s o t h e r m a l s e c t i o n s of the d i a g r a m at 973 and 1273 K (1290 and 1830~ The s i g n i f i e a n t f e a t u r e s of t h e s e d i a g r a m s a r e : 1) the p r e s e n c e of five t y p e s of e a r b i d e s - M 2 C and Mo2C, found in b o t h the b i n a r y and t e r n a r y s y s t e m s and FeeMoC, M23C6 and MsC, found in the t e r n a r y s y s t e m s and 2) the fact that a l l e x c e p t the M6C a r e in e q u i l i b r i u m only with the a u s t e n i t e (V) p h a s e , w h e r e a s the MsC is in e q u i l i b r i u m with both the a u s t e n i t e (~) and the f e r -
L. RICHARD WOODYATT is Engineer, Research Department, Bethlehem Steel Corporatio
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