Temper embrittlement of Ni-Cr steel by antimony: III. Effects of Ni and Cr
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C. J. McMAHON,
Jro, D. P. POPE,
AND
H. C. FENG
The individual effects of Ni and Cr on t e m p e r e m b r i t t l e m e n t in a N i - C r s t e e l doped with Sb were studied by n o t c h e d - b a r t e s t i n g and Auger e l e c t r o n s p e c t r o s c o p y . Nickel i s r e q u i r e d for s i g n i f i c a n t s e g r e g a t i o n of Sb to g r a i n b o u n d a r i e s (and c o n c o m i t a n t e m b r i t t l e m e n t ) . The addition of Cr somehow m a k e s Ni m o r e effective i n this r e s p e c t ; s e g r e g a t i o n of C r was not detected. P r e c i p i t a t i o n of C r - r i c h c a r b i d e s , which depletes the a m a t r i x of Cr, r e d u c e s the e m b r i t t l e m e n t s u s c e p t i b i l i t y . The a m o u n t of s e g r e g a t e d Ni is a f u n c tion only of the a m o u n t of s e g r e g a t e d Sb; it is independent of Cr o r C content of the s t e e l .
IT is
now quite evident that the r o l e played by alloy e l e m e n t s i n the p h e n o m e n o n of t e m p e r e m b r i t t l e m e n t i s j u s t as i m p o r t a n t as that of the m e t a l l o i d e m b r i t t l i n g e l e m e n t s . This was f i r s t d e m o n s t r a t e d by Low e t al 1 i n a study of e m b r i t t l e m e n t of N i - C r , N i - o n l y , and C r only s t e e l s by Sb, Sn, As, and P . The alloy effects a r e now u n d e r s t o o d to be a r e s u l t of: 1) the a t t r a c t i v e i n t e r a c t i o n s b e t w e e n alloy and m e t a l l o i d e l e m e n t s 2"~ and 2) the influence of alloy e l e m e n t s on h a r d e n a b i l i t y and r e s i s t a n c e to s o f t e n i n g d u r i n g t e m p e r i n g . 5 In the p r e s e n t p a p e r , v a r i a t i o n s in the Ni, Cr, and C contents in the o f t e n - s t u d i e d N i - C r s t e e l doped with Sb 1'3-6 a r e e x a m i n e d with the b e n e f i t of A u g e r e l e c t r o n s p e c t r o s copy in o r d e r to s o r t out the effects of these e l e m e n t s on t e m p e r e m b r i t t l e m e n t by Sb. EXPERIMENTAL
PROCEDURES
The alloys used for this study were vacuum melted at the General Electric Research and Development Center, using high purity melting practice. They were hot forged into 2.54 cm or 1.27 cm diam bars and then hot swaged to 0.635 cm diam. The alloy compositions are given in Table I; they are similar to the alloys studied by Low et al.* The high carbon specimens were austenitized I h at 1200~ (1473 K) under a dynamic vacuum of 50 x I0 -3 Torr (6.7 Pa) and oil quenched. Specimens were then tempered in evacuated Vycor capsules at 625~ (898 K) for 1 h (unless otherwise noted), water quenched, and then isothermally embrittled at 480~ (753 K) or 520~ (793 K). The Ni-only low carbon steel was recrystallized at 650~ (923 K) for I00 h after having been annealed at 1000~ (1273 K) and cold swaged; it was then embrittled as above. Round bar specimens machined to 0.584 cm diam were used to measure transition temperatures using a slow bend technique described elsewherefl A u g e r e l e c t r o n s
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