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l i f e b y a s much a s 60 p c t ( T a b l e I). A t y p i c a l m a c r o p h o t o g r a p h of a f r a c t u r e s u r f a c e of h y d r o g e n e m b r i t t l e d HY-130 s t e e l is shown in Fig. 2(a), along with the u n e m b r i t t l e d HY-130 s t e e l s p e c i m e n in F i g . 2(b). The m a i n d i f f e r e n c e b e t w e e n the f r a c t u r e s u r f a c e s of the Y. G. KIM AND J. A L E S Z K A h y d r o g e n - e m b r i t t l e d s p e c i m e n s and the u n e m b r i t t l e d s p e c i m e n s is the p a r a b o l i c - c o n t o u r s in the fatigue The p r o b l e m of h y d r o g e n e m b r i t t l e m e n t in m e t a l s z o n e s a d j o i n i n g the notch of the e m b r i t t l e d s p e c i m e n s . has received considerable attention by many investiThe s a m e s u r f a c e c o n t o u r s w e r e a l s o o b s e r v e d in the g a t o r s . ~-s The g e n e r a l m a n i f e s t a t i o n s of h y d r o g e n e m fatigue zone of the h y d r o g e n - e m b r i t t l e d T - 1 s t e e l s a m b r i t t l e m e n t a r e s h a r p l o s s e s in d u c t i l i t y and s t r e n g t h . p l e s (Fig. 3(a)). Such f e a t u r e s w e r e not o b s e r v e d in the E m b r i t t l e m e n t i s m o s t s e v e r e at about r o o m t e m p e r a fatigue zone of the u n e m b r i t t l e d T - 1 s t e e l s a m p l e s (Fig. t u r e and d e c r e a s e s with i n c r e a s i n g s t r a i n r a t e and d e 3(5)). c r e a s i n g t e m p e r a t u r e . The d e g r e e of e m b r i t t l e m e n t Scanning e l e c t r o n m i c r o s c o p y w a s a l s o used to i d e n g e n e r a l l y i n c r e a s e s with i n c r e a s i n g t e n s i l e s t r e n g t h tify the t o p o g r a p h y of the fatigue zone u s i n g a s t e r e o in i r o n - b a s e a l l o y s and with i n c r e a s i n g h y d r o g e n c o n v i e w i n g technique. S t e r e o f r a c t o g r a p h s of HY-130 tent (up to 5 ppm). Thus, h y d r o g e n e m b r i t t l e m e n t b e s t e e l , F i g . 4(a) and (b), and T - 1 s t e e l , F i g . 5(a) and c o m e s m o r e of a p r o b l e m when h i g h - s t r e n g t h s t e e l s (b), r e v e a l e d that the fatigue zone of h y d r o g e n - e m containing h y d r o g e n o r e x p o s e d to h y d r o g e n e n v i r o n b r i t t l e d s a m p l e s d i s p l a y e d a d i s p e r s i o n of c r a t e r s . m e n t s a r e u s e d in e n g i n e e r i n g a p p l i c a t i o n s . Each c r a t e r u s u a l l y c o n t a i n s one o r m o r e m i c r o Hydrogen can b e i n t r o d u c e d into m e t a l s by a n u m b e r c r a c k s . T h e s e l o n g i t u d i n a l m i c r o c r a c k s a p p e a r to of p r o c e s s e s , s u c h a s m e l t i n g , c a s t i n g , welding, c o r r o be a s s o c i a t e d with the b a n d e d s t r u c t u r e r e s u l t i n g f r o m sion and e l e c t r o p l a t i n g . The m a j o r i t y of i n v e s t i g a t i o n s the r o l l i n g o p e r a t i o n s . On the o t h e r hand, no c r a t e r s of h y d r o g e