Grain size vs ductile-brittle transition in an Fe-12 pct Ni alloy
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Grain Size Vs Ductile-Brittle Transition in an Fe-12 Pct Ni Alloy GO SASAKI AND MICHAEL J. YOKOTA In a n u m b e r of c o m m u n i c a t i o n s to this j o u r n a l , 1-3 the question of a s t r o n g v s a weak dependence of the d u c t i l e - b r i t t l e t r a n s i t i o n t e m p e r a t u r e (DBTT) on g r a i n s i z e in i r o n and F e - N i alloys has b e e n debated. L e s l i e , e t a l . 4 r e a s o n e d that r e m o v a l of i n t e r s t i t i a l s o l u t e s b y the addition of t i t a n i u m to i r o n e l i m i n a t e d most of the g r a i n size dependence of notch i m p a c t r e s i s t a n c e , while Gupta and o t h e r s 1'2 a r g u e d that a s t r o n g e r r e l a tionship existed. But when L e s l i e 3 plotted the data a v a i l a b l e f r o m the m o s t r e c e n t s t u d i e s , t h e i r slopes GO SASAKI,formerly Graduate Student, Inorganic Metals Research Division, Lawrence Berkeley Laboratory, University of Berkeley, is now with Bechtel Corporation, Scientific Development and Materials Fabrication and Quality Control Service, San Francisco, Calif. 94119. MICHAEL J. YOKOTA is Research Metallurgist,Department of Materials Science and Engineering,College of Engineering, University of California, Berkeley, Calif. 94720. Manuscript submitted August 8, 1974. 586-VOLUME 6A, MARCH 1975
Fig. 1--Fe-12 pct Ni-0.3 pct Ti austenitized at 900~ for 2 h and water quenched: (a) bight micrograph, (b) scanning electron rnicrograph of Charpy V-notch specimen broken at LN temperature. all fell within a n a r r o w 6 to 7 K p e r m m -~/z r a n g e . We r e p o r t h e r e the g r a i n size dependence of the d u c t i l e b r i t t l e t r a n s i t i o n t e m p e r a t u r e for s t a n d a r d full size Charpy V-notch s p e c i m e n s of an F e - 1 2 pct Ni-0.3 pct Ti alloy. This alloy d i f f e r s f r o m the i r o n and F e - l o w Ni a l l o y s e x a m i n e d p r e v i o u s l y in that when it is quenched f r o m the a u s t e n i t e phase a m a r t e n s i t i c r a t h e r than a f e r r i t i c s u b s t r u c t u r e is f o r m e d . An e x a m p l e of the lath m a r t e n s i t e s t r u c t u r e t y p i c a l of F e - h i g h Ni alloys is shown in Fig. l(a). The s m a l l e r a r e a s within each p r i o r a u s t e n i t e g r a i n exhibiting diff e r e n t etching c h a r a c t e r i s t i c s a r e lath packets, within which the m a r t e n s i t e laths a r e a r r a n g e d r o u g h l y p a r a l l e l to each other. Fig. 2 shows the laths to have widths that v a r y between 0.5 and 1.0 p m and to contain a d i s l o c a t i o n , d e n s i t y of about 1011 to 10~2/cm 2. The a u s t e n i t e g r a i n r a t h e r than the lath packet size METALLURGICALTRANSACTIONSA
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