Hydrogen performance of precipitation-strengthened stainless steels based on A-286
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W. THOMPSON
AND
JOHN
A. BROOKS
Eleven a l l o y s s i m i l a r to c o m m e r c i a l A-286 but with s m a l l v a r i a t i o n s in c h e m i s t r y w e r e t e s t e d to a s s e s s w h e t h e r the p e r f o r m a n c e of t h i s type of s t a i n l e s s s t e e l , which shows a d u c t i l i t y (RA) l o s s of about 48 p c t when h y d r o g e n c h a r g e d , could be i m p r o v e d . It w a s found t h a t r e m o v a l of Mn r e s u l t e d in an RA l o s s of only 15 pct; low Mn p l u s a 5 p c t i n c r e a s e in Ni gave f u r t h e r i m p r o v e m e n t to 11 p c t RA l o s s . R e d u c t i o n s in C, Si and B had l i t t l e e f f e c t on t h e s e RA l o s s e s . None of the above c h a n g e s had s i g n i f i c a n t e f f e c t on s t r e n g t h . Other c h e m i s t r y c h a n g e s w e r e u n s u c c e s s f u l : a d d i t i o n s of A1, Ti, Ti + Mo, o r d e c r e a s e s in Ni, i n c r e a s e d the d u c t i l i t y l o s s . E x t e n s i v e e x a m i n a t i o n of thin f o i l s p e r m i t t e d a s t r u c t u r a l r a t i o n a l e f o r b e h a v i o r in h y d r o g e n in t e r m s of the e f f e c t s of s e c o n d p h a s e p a r t i c l e s on d u c t i l e f r a c t u r e , p a r t i c u l a r l y a s a f f e c t e d by the m i s f i t b e t w e e n the a u s t e n i t e and the Y' p r e c i p i t a t e s . This r a t i o n a l e was c o n s i s t e n t with f r a c t o g r a p h i c o b servations.
THE demand for structural materials suitable for s e r v i c e in h y d r o g e n o r h y d r o g e n - b e a r i n g e n v i r o n m e n t s , such a s p r o d u c t i o n of s y n t h e t i c c o a l g a s e s , ~ e n e r g y t r a n s m i s s i o n in a " h y d r o g e n e c o n o m y , " ~'2 o r s t o r a g e of o f f - p e a k e n e r g y a s h y d r o g e n gas, 3 can be e x p e c t e d to i n c r e a s e m a r k e d l y in the f o r e s e e a b l e f u t u r e . Yet the p r e s e n t l i s t of a c c e p t a b l e m a t e r i a l s , a s s u m i n g that r e s i s t a n c e to h y d r o g e n e m b r i t t l e m e n t and d e l a y e d f a i l u r e is a p a r a m o u n t c r i t e r i o n f o r a c c e p t a b i l i t y , is not only s h o r t but is l i m i t e d to m a t e r i a l s of r e l a t i v e l y low s t r e n g t h . 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 , f o r e x a m p l e , have p r o v e n in s e v e r a l i n s t a n c e s to be only m i l d l y d a m a g e d b y h y d r o g e n , 4 - n but a r e t y p i c a l l y no s t r o n g e r than 500 M N / m 2 (about 75 k s i ) y i e l d s t r e n g t h . 7 - n T h e r e a r e e x p e c t e d to be a v a r i e t y of a p p l i c a t i o n s in h y d r o g e n , i n c l u d i n g p u m p s , v a l v e s and o t h e r p a r t s , which will d e m a n d h i g h e r s t r e n g t h . Thus, an a u s t e n i t i c m a t r i x s t r e n g t h e n e d b y p r e c i p i t a tion m i g h t be s e l e c t e d to o f f e r not o n l y h i g h e r s t r e n g t h , but a c c e p t a b l e h y
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