The effect of austenite prestrain above the M d temperature on the martensitic transformation in Fe-Ni-Cr-C alloys
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THE
effect of a u s t e n i t e p r e s t r a i n on the s u b s e q u e n t m a r t e n s i t i c t r a n s f o r m a t i o n has r e c e i v e d c o n s i d e r a b l e a t t e n t i o n s i n c e the d i s c o v e r y of a u s f o r m i n g as an i m p r o v e d h a r d e n i n g technique for low alloy s t e e l s in 1954 by Lips and Van Z u i l e n . ~ N u m e r o u s i n v e s t i g a t i o n s 2-~~ of the ~tusforming p r o c e s s w e r e conducted in the late I 9 5 0 ' s and e a r l y 1960's with the m a i n m e t a l l u r g i c a l i n t e r e s t c e n t e r e d on the o p t i m i z a t i o n of p r o cess p a r a m e t e r s f r o m a m a t e r i a l p r o p e r t y s t a n d point. A t t e m p t s to a n a l y z e the r e s u l t s of t h e s e i n v e s tigations from a fundamental standpoint were complicated by the high M s t e m p e r a t u r e s of the m a t e r i a l s studied which made the d e t e r m i n a t i o n of the effect of d e f o r m a t i o n on the M s , k i n e t i c s , and s t r u c t u r e of the s u b s e q u e n t t r a n s f o r m a t i o n e x p e r i m e n t a l l y difficult. In a m o r e r e c e n t i n v e s t i g a t i o n , B r i e n a n and A n s e l l z~ d e s i g n e d a high t e m p e r a t u r e t e n s i l e a p p a r a t u s which allowed the m o n i t o r i n g of the t r a n s f o r m a t i o n in s i m i l a r a l l o y s following d e f o r m a t i o n . They d e f o r m e d a 5 pct C r tool s t e e l above the M d t e m p e r a t u r e and c o r r e l a t e d i n c r e a s e d p r e s t r a i n with a d e c r e a s e in both the M s and the p e r c e n t t r a n s f o r m e d at r o o m t e m p e r a t u r e . The effect of p r e s t r a i n on the m a r t e n s i t i c s t r u c t u r e was not d e t e r m i n e d . T h o m a s e t a112 r e l a t e d p r i o r a u s t e n i t e d e f o r m a t i o n to changes in m a r t e n s i t e s t r u c t u r e in a s e r i e s of alloys with M s below r o o m t e m p e r a t u r e . I n c r e a s e d a u s t e n i t e p r e s t r a i n was shown to d e c r e a s e the a m o u n t of twinned m a r t e n s i t e t r a n s f o r m e d on q u e n c h ing. However, this r e s u l t was due m a i n l y to alloy c a r bide p r e c i p i t a t i o n d u r i n g d e f o r m a t i o n which depleted the m a t r i x of c a r b o n and r a i s e d M s . T h u s , a s i m p l e c o r r e l a t i o n with a u s t e n i t e p r e s t r a i n could not be made. T h e r e a r e also a n u m b e r of i n v e s t i g a t i o n s which have u t i l i z e d a u s t e n i t e p r e s t r a i n effects on the s u b s e J. R. STRIFE is Materials Scientist, Central Scientific Laboratory, Union Carbide Corporation, Tarrytown, NY 10591, M. J. CARR is Semor Research Metallurgist, Rockwell International, Golden, CO 80401 and G. S. ANSELL is Dean, School of Engineenng, Rensselaer Polytechnic Institute, Troy, NY 12180. Manuscript submitted December 6, 1976. METALLURGICALTRANSACTIONSA
quent t r a n s f o r m a t i o n as an a p p r o a c h to b e
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