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The i n t e r n a l n i t r i d a t i o n of thin s e c t i o n s of a u s t e n i t i c F e - C r - N i - T i a l l o y s containing up to 2 pct T i was s t u di e d o v e r the t e m p e r a t u r e r a n g e 1600 ~ to 2210~ in o r d e r to d ev el o p a m e t h o d of s t r e n g t h e n i n g the a l l o y s through the i n t r o d u c t i o n of a d i s p e r s o i d of stable t i t a n i u m n i t r i d e s . The i n t e r p a r t i c l e s p a c in g (IPS) of the n i t r i d e s was found to i n c r e a s e l i n e a r l y with depth f r o m the e x t e r n a l s u r f a c e ; the e f f e c t s of v a r i o u s p a r a m e t e r s on the r a t e of change of IPS vs depth a r e p r e s e n t e d . The m e c h a n i c a l p r o p e r t i e s of t h e s e a l l o y s at r o o m and e l e v a t e d t e m p e r a t u r e s w e r e m a r k e d l y i m p r o v e d by i n t e r n a l l y n i t r i d i n g . Useful m e c h a n i c a l p r o p e r t i e s w e r e obtained up to 2200~ with t y p i c a l p r o p e r t i e s at 2000~ of 10 to 20 ksi 0.2 pct offset y i e l d s t r e n g t h and 15 to 25 ksi u l t i m a t e t e n s i l e s t r e n g t h , but s e c t i o n t h i c k n e s s was l i m i t e d to about 10 m i l s b e c a u s e of the i n c r e a s e in IPS with depth and the long n i t r i d i n g t i m e s n e e d e d f o r t h i c k e r m a t e r i a l . In o r d e r to p r o d u c e a s m a l l i n t e r p a r t i c l e s p a c i n g in a h e a v i e r s e c t i o n , i n t e r n a l l y n i t r i d e d 5 m i l s t r i p was c o n s o l i d a t e d by hot r o l l bonding and e v a l u a t e d at a 60 m i l t h i c k n e s s by t e n s i l e and r u p t u r e t e s t i n g at 2000~ It is d e m o n s t r a t e d that the a p p r o a c h taken in this work o f f e r s a f e a s i b l e technique f o r m a k i n g a high t e m p e r a t u r e al l o y having useful engineering properties.

AUSTENITIC

s t a i n l e s s s t e e l s a r e c h a r a c t e r i z e d by good f o r m i n g c h a r a c t e r i s t i c s and have t r a d i t i o n a l l y b e e n u s e d f o r c o r r o s i o n and oxidation r e s i s t a n c e . Howe v e r , a l l o y s of t h i s c l a s s a r e weak a t t e m p e r a t u r e s above about 1200~ w h e r e r e c r y s t a l l i z a t i o n can o c c u r , ~ and p o s s e s s little p r a c t i c a l s t r e n g t h at t e m p e r a t u r e s in e x c e s s of 1700~ 2 m a k i n g t h e m unsuitable for high t e m p e r a t u r e s t r u c t u r a l a p p l i c a t i o n s . The o b j e c t i v e of t h i s work was the i n v e s t i g a t i o n of a m e t h o d of d i s p e r sion s t r e n g t h e n i n g a u s t e n i t i c s t a i n l e s s s t e e l a l l o y s to a c h i e v e useful high t e m p e r a t u r e m e c h a n i c a l p r o p e r t i e s f o r s e r v i c e a p p l i c a t i o n s to 2000~ The a p p l i c a t i o n of d i s p e r s i o n s t r e n g t h e n i n g f o r the d e v e l o p m e n t of high t e m p e r a t u r e s t r u c t u r a l a l l o y s has c e n t