Hydrogen enhanced crack growth in 18 Ni maraging steels
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d e l e t e r i o u s effect of h y d r o g e n on the m e c h a n i c a l p r o p e r t i e s of s t e e l s , e s p e c i a l l y h i g h - s t r e n g t h m a r t e n s i t i c s t e e l s , i s a w e l l known p r o b l e m in the a r e a of e n v i r o n m e n t - s e n s i t i v e m e c h a n i c a l b e h a v i o r of m a t e r i a l s . This phenomenon, c o m m o n l y t e r m e d h y d r o g e n e m b r i t t l e m e n t , i s of c o n c e r n o v e r a b r o a d t e c h n o l o g i c a l r a n g e - p r o d u c t i o n , m a n u f a c t u r i n g , and s e r v i c e . C o m m o n p r o c e s s e s , such a s s t e e l m a k i n g , 1'2 welding, 3 e l e c t r o p l a t i n g , ~'7 p i c k l i n g , 8 and c o r r o s i o n , ~'n a r e p o t e n t i a l l y e m b r i t t l i n g s i n c e a l l a r e c a p a b l e of l i b e r a t i n g d e t r i m e n t a l h y d r o g e n u n d e r c e r t a i n conditions. E m b r i t t l e m e n t that r e s u l t s f r o m the a b o v e p r o c e s s e s is g e n e r a l l y r e f e r r e d to a s " i n t e r n a l h y d r o g e n e m b r i t t l e m e n t " . T h i s f o r m of e m b r i t t l e m e n t is d i f f e r e n t i a t e d from "hydrogen environment embrittlement", or gaseous h y d r o g e n e m b r i t t l e m e n t , w h e r e b y s t e e l s a r e e m b r i t t l e d a s a r e s u l t of e x p o s u r e to g a s e o u s h y d r o gen. G a s e o u s h y d r o g e n e m b r i t t l e m e n t can o c c u r o v e r a wide r a n g e of h y d r o g e n p r e s s u r e s , down to t e n s of T o r r . 11-22 T h i s b r o a d r a n g e of s u s c e p t i b i l i t y p o s e s p r o b l e m s in n u m e r o u s s e r v i c e s i t u a t i o n s . The c u r r e n t i n v e s t i g a t i o n is d i r e c t e d at this e l e m e n t of the e m b r i t t l e m e n t phenomenon, n a m e l y that of g a s e o u s hydrogen embrittlement. The w i d e s p r e a d o c c u r r e n c e s of s e r v i c e f a i l u r e s due to h y d r o g e n e m b r i t t l e m e n t h a s p r o v i d e d the i m p e t u s f o r n u m e r o u s i n v e s t i g a t i o n s of the p r o b l e m o v e r the p a s t fifty y e a r s . The focus of technology o v e r m o s t of this p e r i o d w a s such that a g r e a t m a j o r i t y of t h e s e i n v e s t i g a t i o n s d e a l t with i n t e r n a l h y d r o g e n e m b r i t t l e m e n t . In s p i t e of t h e s e e f f o r t s , a b a s i c u n d e r s t a n d i n g of the a c t u a l e m b r i t t l e m e n t m e c h a n i s m r e m a i n s e l u s i v e . E m b r i t t l e m e n t by g a s e o u s h y d r o g e n h a s b e c o m e a s e r i o u s p r o b l e m m o r e r e c e n t l y , and has r e c e i v e d a t t e n t i o n l a r g e l y through the a e r o -
S. J. HUDAK, Jr. is Research Engineer, Westinghouse Research Laboratories, Pittsburgh, PA 15235. R. P. WEI is Professor of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA 18015, where S. J. Hudak Jr. was formerly a Graduate Student and Research
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