On the Effect of Carbon on the Stacking Fault Energy of Austenitic Stainless Steels
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On the Effect of Carbon on the Stacking Fault Energy of Austenitic Stainless Steels
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P, J. BROFMAN
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G. S. ANSELL
In a r e c e n t w o r k by S c h r a m m and R e e d , 1 s t a c k i n g fault e n e r g y (SFE) d a t a found in the l i t e r a t u r e for a u s t e n i t i c s t a i n l e s s s t e e l s was l i n e a r l y c o r r e l a t e d with e l e m e n t a l c o m p o s i t i o n . Since s t a c k i n g fault e n e r g y in t h e s e a l l o y s h a s both c o m m e r c i a l and t h e o r e t i c a l significance, accurate compositional correlations are extremely important. S p e c i f i c a l l y , the following c o r r e l a t i o n (Eq. 8(a) of R e f . 1) was found b e t w e e n S F E and weight p e r c e n t Ni, C r , and C:
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6'0 10 20 30 40 50 WEIGHT PERCENT COMPOSITIONEOUIVALENT [16.7* 2.1(%Ui)-0-9P/oCr) * 2~/oC)]
[1]
H o w e v e r , the high value of the c o e f f i c i e n t a s s i g n e d to c a r b o n is in c o n t r a s t to the o b s e r v a t i o n by S c h r a m m and R e e d 1 that c a r b o n , d e s p i t e its a b i l i t y to p r o m o t e c e I l u l a r d i s l o c a t i o n a r r a y s , has b e e n r e p o r t e d to have l i t t l e o r no effect on S F E . 2's T h e s e a u t h o r s 1 f u r t h e r q u e s t i o n the v a l i d i t y of Eq. [1] by p o i n t i n g out the s i g n i f i c a n t l y d i f f e r e n t value for the c o n s t a n t ( c o r r e s p o n d ing to the e x t r a p o l a t e d S F E of p u r e FCC i r o n at r o o m t e m p e r a t u r e ) obtained for o t h e r c o m p o s i t i o n a l c o r r e l a t i o n s . (i.e., this c o n s t a n t a v e r a g e s about 33 for the N i - C r - N , N i - C r - S i , and N i - C r - M n c o m p o s i t i o n s e r i e s , c o m p a r e d to 4 in the above N i - C r - C c a s e . See E q s . 8(a) to (d) in Ref. 1.) Of the s e v e n a l l o y s u s e d to e s t a b l i s h Eq. [1], the m a x i m u m c a r b o n content was only 0.036 pct. S t r i f e et al 4 have r e c e n t l y p u b l i s h e d S F E d a t a for a u s t e n i t i c s t a i n l e s s s t e e l s having n e a r l y 0.3 p c t C (See T a b l e I). A b r a s s a r t S a d d i t i o n a l l y p r o v i d e s d a t a for an 0.18 p c t C s t e e l . C a s u a l o b s e r v a t i o n i n d i c a t e s that t h e s e h i g h e r c a r b o n a l l o y s do not fit the S c h r a m m and R e e d c o r r e lation. A f o u r - d i m e n s i o n a l l i n e a r r e g r e s s i o n a n a l y s i s , including t h e s e a l l o y s of h i g h e r c a r b o n content, was c o m p u t e d in a m a n n e r s i m i l a r to that of S c h r a m m and R e e d . 1 The d a t a u s e d for this a n a l y s i s , shown in T a b l e I, r e p r e s e n t a l l o y s in the r a n g e 9 to 20 pct C r , 5 to 20 pct Ni, up to 0.29 pct C, and l e s s than 0.1 p c t o t h e r e l e m e n t s . Only t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y (TEM) s t a c k i n g fault e n e r g y d a t a u
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