Effect of the nature of imperfections on the precipitation of M 23 C 6 carbide in austenitic steels
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METALLURGICAL TRANSACTIONS
1. F. D. Rosiand F. C. Perkins: Trans. ASM, 1953, vol.45, pp. 972-91. 2. B. Sesta'k: Theory of CrystalDefects, pp. 357-402, AcademicPress, NewYork, 1966. 3. A. R. Rosenfieldand W. S. Owen:Symposium on the Role of Substructures in the Mechanical Behavior of Metals, pp. 351-74, Tech. Doc. Dept. No. ASD-TDR63-324, Directorateof Materialsand Processes,Wright-PattersonAir ForceBase, Ohio, April 1963. 4. J. W. Edington, T. C. Lindley,and R. E. Smallman:Acta. Met., 1964, vol. 12, pp. 1025-31. 5. H. E. Rosingerand G. B. Craig:ScriptaMet., 1969,vol. 3, pp. 301-05. 6. R. J. Wasilewskiand G. L. Kehl:J. Inst. Metals, 1954, vol. 83, pp. 94-104. 7. J. E, Reynolds,H. R. Ogdenand R. I. Jaffee: Trans. ASM, 1957, vol.49, pp. 280-99. 8. W. S. Owenand M. J. Roberts: Dislocation Dynamics, pp. 357-78, McGraw-Hill, NewYork, 1968.
Effect of the Nature of Imperfections on the Precipitation of M23C 6 Carbide in Austenitic Steels L.K.
SINGHAL
IT
is now w e l l - e s t a b l i s h e d that i m p e r f e c t i o n s such a s v a c a n c i e s , d i s l o c a t i o n s , s t a c k i n g f a u l t s , and g r a i n b o u n d a r i e s h a v e a p r o n o u n c e d i n f l u e n c e on the n u c l e a tion and g r o w t h of p r e c i p i t a t e s . 1 M o r p h o l o g y of h e t e r o g e n e o u s p r e c i p i t a t e s is q u i t e o f t en o b s e r v e d to depend on the s i t e s of its n u c l e a t i o n and the p r e s e n t w o r k w a s a i m e d at e l u c i d a t i n g t h e v a r i a t i o n s in t h e m o d e of f o r m a t i o n and m o r p h o l o g y of M2aCe p r e c i p i t a t e s in a u s tenite. An a l l o y A , T a b l e I, with a n o m i n a l c o m p o s i t i o n of F e , 2 5 C r , 2 4 N i , 0 .0 4 C w a s u s e d f o r d e t a i l e d e x a m i n a t i o n . A n o t h e r a l l o y B c o n t a i n i n g an a d d i t i o n a l a m o u n t of 0.3 pet Ti w a s u s e d f o r c o m p a r i s o n . The r e s u l t s of o u r i n v e s t i g a t i o n s on MzaC6 p r e c i p i t a t i o n in t h e s e a l l o y s a r e p r e s e n t e d in T a b l e II. In t h i s note s o m e i n t e r e s t i n g f e a t u r e s of p r e c i p i t a t i o n on c o h e r e n t twin b o u n d a r i e s and in r e g i o n s c l o s e to g r a i n b o u n d a r i e s h a v e b e e n discussed. A l l o y s t r i p s w e r e s e a l e d in s i l i c a t u b es u n d e r 15 c m a r g o n and s o l u t i o n heat t r e a t e d at 1150~ f o r 3 h r f o l lowed by a q u e n c h into an i c e - w a t e r m i x t u r e . Aging w a s c a r r i e d out in s e a l e d s i l i c a t u b e s at 650 ~ and 7 50~ Th e method f o r p r e p a r a t i o n of thin f o i l s is g iv en e l s e w h e r e . 5 M e t a l l o g r a p h i e e x a m i n a t i o n w a s c a r r i e d out in t h e A . E . I . EM 6 e l e c t r o n m i c r o s c o p e . P R E C I P I T A T I O N ON C O H E R E N T TWIN BOUNDARIES T h i n s h e e t s of MzsC6 c a r b i d e p r e c i p i t a t e s lying on the twin b o u n d a r i e s a r e g e n e r a l l y o b
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