The volume expansion accompanying the martensite transformation in iron-carbon alloys
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AND
G. S. ANSELL
A d i l a t o m e t r i c i n v e s t i g a t i o n w a s conducted to d e t e r m i n e the effect of c a r b o n on the v o l u m e e x p a n s i o n a c c o m p a n y i n g the m a r t e n s i t e t r a n s f o r m a t i o n in i r o n - c a r b o n a l l o y s . It w a s found that the v o l u m e e x p a n s i o n at the M s t e m p e r a t u r e v a r i e s f r o m 2.0 p c t at 0.19 wt pct c a r b o n to 3.1 p c t a t 1.01 p c t c a r b o n , l a r g e l y due to the effect of c a r b o n on l o w e r i n g the t e m p e r a t u r e at which the t r a n s f o r m a t i o n o c c u r s . Also of i m p o r t a n c e is the s o l i d s o l u t i o n effect of c a r b o n on a l t e r i n g the l a t t i c e p a r a m e t e r s of both the a u s t e n i t e and m a r t e n s i t e p h a s e s at the M s .
A L T H O U G H it has long been r e c o g n i z e d that a v o l ume e x p a n s i o n o c c u r s a s f e r r o u s a u s t e n i t e t r a n s f o r m s to m a r t e n s i t e , a s y s t e m a t i c i n v e s t i g a t i o n has n e v e r been conducted to d e t e r m i n e e i t h e r the individual o r c o l l e c t i v e e f f e c t s of a l l o y i n g e l e m e n t s on the v o l u m e e x p a n s i o n in s t e e l s . The amount of v o l u m e e x p a n s i o n o c c u r r i n g d u r i n g the m a r t e n s i t e r e a c t i o n is often a s s u m e d to be uninfluenced b y c a r b o n content, ha's and e i t h e r a s s i g n e d a c o n s t a n t v a l u e ( i . e . 4 p c t 2 o r 5 p c t 3) o r a s s u m e d to l i e within s o m e r a n g e of v a l u e s ( i . e . 3 to 4 p c t 4 o r 3 to 5 pctS). Thus the v o l u m e e x p a n s i o n h a s often b e e n c o n s i d e r e d i n d e p e n d e n t of c o m p o s i t i o n and t r a n s f o r m a t i o n t e m p e r a t u r e , although d a t a to the contrary exist. Using s p e c i f i c v o l u m e d a t a f r o m i r o n - c a r b o n a l l o y s and c o m m e r c i a l p l a i n c a r b o n s t e e l s , Hollomon and Jaffe 6 c a l c u l a t e d the v a r i a t i o n of the v o l u m e e x p a n s i o n with t r a n s f o r m a t i o n t e m p e r a t u r e and concluded that it i n c r e a s e s l i n e a r l y with d e c r e a s i n g t r a n s f o r m a t i o n t e m p e r a t u r e , f r o m 2.3 pct at 540~ to 4.0 p c t at 90~ H o u d r e m o n t and K r i s e m e n t 7 m a d e s i m i l a r c a l c u l a t i o n s using room temperature iron-carbon lattice parameter d a t a a s w e l l a s u n d i s c l o s e d t h e r m a l e x p a n s i o n data, and found the v o l u m e e x p a n s i o n at the M s t e m p e r a t u r e s in t h e s e a l l o y s to be n e a r l y c o n s t a n t at 2.8 pct. Using a d i l a t o m e t e r , Mcgee and D a v i e s 8 m e a s u r e d the v o l u m e e x p a n s i o n in i r o n - n i c k e l - c o b a l t a l l o y s at t h e i r M s t e m p e r a t u r e s and found that in t h o s e a l l o y s which exhibit i n v a r a u s t e n i t e b e h a v i o r , the v o l u m e e x pansion was s
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