The relationship between austenite strength and the transformation to martensite in Fe-10 pct Ni-0.6 pct C alloys
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S E V E R A L i n v e s t i g a t o r s 1-7 have d i s c u s s e d the r e l a t i o n s h i p b e t w e e n the r e s i s t a n c e to p l a s t i c d e f o r m a t i o n of the a u s t e n i t e and the n a t u r e of the a u s t e n i t e to m a r t e n s i t e t r a n s f o r m a t i o n . T h e a u s t e n i t e to m a r t e n s i t e t r a n s f o r m a t i o n o c c u r s when the c h e m i c a l f r e e e n e r g y d e c r e a s e a c c o m p a n y i n g the t r a n s f o r m a t i o n ( i . e . , f r e e e n e r g y of a u s t e n i t e m i n u s f r e e e n e r g y of m a r t e n s i t e ) i s e q u a l to o r l a r g e r than the e n e r g y n e c e s s a r y to o v e r c o m e the r e s i s t a n c e to v o l u m e d e f o r m a t i o n , s t r a i n e n e r g y and the c r e a t i o n of new s u r f a c e s which a c c o m p a n y the t r a n s f o r m a t i o n . T h e r e s i s t a n c e of a u s t e n i t e to p l a s t i c d e f o r m a t i o n has b e e n c o n s i d e r e d to c o n t r i b u t e to the magnitude of this n o n c h e m i c a l f r e e e n e r g y t e r m J T h e p r e c i s e n a t u r e of the c o n t r i b u t i o n h a s not b e e n i s o l a t e d p r i m a r i l y b e c a u s e the m e t h o d s that v a r y the a u s t e n i t e y i e l d s t r e n g t h , e . g . , s o l i d s o l u tion s t r e n g t h e n i n g , w o r k h a r d e n i n g and p r e c i p i t a t i o n h a r d e n i n g , r e s u l t in s i m u l t a n e o u s changes in e i t h e r the c h e m i c a l f r e e e n e r g y o r the n u c l e a t i o n k i n e t i c s f o r the t r a n s f o r m a t i o n . In addition, m o s t of the s t u d i e s have not a c t u a l l y m e a s u r e d the a u s t e n i t e y i e l d s t r e n g t h p r i o r to t r a n s f o r m a t i o n . T h e e f f e c t s of a l l o y i n g a d d i t i o n s on the c h e m i c a l d r i v i n g f o r c e for the a u s t e n i t e to m a r t e n s i t e t r a n s f o r m a t i o n a r e w e l l known. The effects of a l l o y i n g a d d i tions on the n o n c h e m i c a l p o r t i o n o r r e s t r a i n i n g f o r c e have a l s o b e e n shown. ~ Yeo showed that the e f f e c t of an a l l o y i n g e l e m e n t w a s not n e c e s s a r i l y unique but d e p e n d e d upon the p r o p e r t i e s of the b a s e a l l o y to which a d d i t i o n s a r e m a d e . He d e m o n s t r a t e d that a l l o y i n g a d d i t i o n s had both c h e m i c a l and m e c h a n i c a l e f f e c t s and d e s c r i b e d the m e c h a n i c a l e f f e c t a s a s t i f f e n i n g of the l a t t i c e a g a i n s t the s h e a r t r a n s f o r m a t i o n thus l o w e r ing the M s . B r e i n a n and A n s e l l , 1 f o r a s e r i e s of a l l o y s t e e l s , u s 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 and T. J. NICHOL is Market Development Manager, Market and Product Development, Allegheny Ludlum Steel Corporation Research Center, Brackenridge, PA 15014, G. JUDD is Vice Provost, and G. S. ANSELL is Dean
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