The effect of reverted austenite on the mechanical properties and toughness of 12 Ni and 18 Ni (200) maraging steels
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T H E e f f e c t s of r e v e r t e d a u s t e n i t e on the m e c h a n i c a l p r o p e r t i e s and t o u g h n e s s of m a r a g i n g s t e e l s is s o m e w h a t c o n t r a d i c t o r y in the l i t e r a t u r e . It has b e e n s t a t e d 1 that although r e v e r t e d a u s t e n i t e m a y i m p r o v e f a b r i c a b i l i t y if i n t r o d u c e d at an i n t e r m e d i a t e s t a g e of p r o c e s s i n g , it should be e l i m i n a t e d by cold w o r k o r r e a n n e a l i n g . H o w e v e r , F l o r e e n ~ has s u g g e s t e d that the p r e s e n c e of a u s t e n i t e in 18 Ni (2505 m a r a g i n g s t e e l could e x p l a i n i t s h i g h e r t o u g h n e s s r e l a t i v e to o t h e r g r a d e s of m a r a g i n g s t e e l s when c o m p a r e d a t equal s t r e n g t h s . 3-4 T h i s could be c o n n e c t e d to L e g e n d r e ' s finding 5 showing that the u n i f o r m e l o n g a t i o n of t e n s i l e s a m p l e s of a 19 Ni 9 Co 5 Mo m a r a g i n g s t e e l i n c r e a s e d s u b s t a n t i a l l y when the s t e e l w a s h e a t t r e a t e d so that s o m e r e v e r t e d a u s t e n i t e w a s p r o d u c e d . The c o n n e c tion is m a d e through the c o r r e l a t i o n which s e e m s to e x i s t b e t w e e n u n i f o r m e l o n g a t i o n and f r a c t u r e toughn e s s . 8-7 We would l i k e to r e p o r t h e r e s o m e r e s u l t s on the e f f e c t of r e v e r t e d a u s t e n i t e on the m e c h a n i c a l p r o p e r t i e s and t o u g h n e s s of two 12 Ni, 5 C r , 3 Mo (J and A) and a 18 Ni, 8 Co, 3 Mo (200 g r a d e ) (K) maraging steel. M A T E R I A L S AND E X P E R I M E N T A L PROCEDURE T h e two 12 Ni s t e e l s d i f f e r e d in m e l t i n g p r a c t i c e p r o d u c i n g a d i f f e r e n t d i s t r i b u t i o n of i n c l u s i o n s , p r e s u m a b l y not changed f u r t h e r by the s u b s e q u e n t h e a t t r e a t m e n t s . S t e e l J is f r o m a v a c u u m induction m e l t , and s t e e l A f r o m an e l e c t r i c f u r n a c e m e l t . S t e e l K was m e l t e d by v a c u u m induction. The c o m p o s i t i o n of the t h r e e s t e e l s is shown in T a b l e I. A l l aging t r e a t m e n t s w e r e p e r f o r m e d a f t e r a u s t e n i t i z i n g for 2 h a t 850~ and oil quenching. O p t i c a l m i c r o g r a p h s showed i n c l u s i o n s 5 to 10 ~ in s i z e in the t h r e e s t e e l s . In s t e e l s J and K the d i s t a n c e b e C. A. PAMPILLO, formerly with the Department of Metallurgy and
Materials Science, Carnegie-Mellon University, Pittsburgh, Pa., is now Research Physicist, Materials Research Center, Allied Chemical Corporation, Morristown, N. J. 07960. H. W. PAXTON, on leave from Carnegie-Mellon University, is Director, Division of Materials Research, National Science Foundation, Washington, D. C. Manuscript submitted August 27, 1971. METALLURGICAL TRANSACTIONS
tween i n c l u s i o n s is a p p r o x i m a t e l y 150 to 300 t~ and in
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