The effect of steelmaking on the hydrogen attack of carbon steel
- PDF / 2,812,681 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 92 Downloads / 215 Views
PISHKO, M A R V I N M c K I M P S O N , A N D
P A U L G. S H E W M O N
Four n o r m a l i z e d c a r b o n s t e e l s made in d i f f e r e n t w a y s (Si-killed, Al-killed, R E M - t r e a t e d , a n d e l e c t r o s l a g r e f i n e d ) w e r e s t u d i e d t o d e t e r m i n e the r o l e of d i f f e r i n g f i n e i n c l u s i o n s o n the e a r l y s t a g e s o f h y d r o g e n a t t a c k ( H A ) . H y d r o g e n e x p o s u r e s w e r e m a d e a t 4 5 0 ° C (6.5 M P a ) a n d 3 7 5 ° C (7.6 M P a ) . T h e f i r s t s t a g e o f HA i s s h o w n t o be t h e d e v e l o p m e n t of a c l o s e l y s p a c e d (1 t o 2 ~ t m ) a r r a y o f s m a l l b u b b l e s o v e r the f e r r i t e / p e a r l i t e , o r o c c a s i o n a l l y the f e r rite/ferrite b o u n d a r i e s . T h e s e b u b b l e s g r e w t o g e t h e r t o f o r m t e a r s , p r i m a r i l y i n the r o l l i n g p l a n e , l e a d i n g t o m o r e r a p i d e x p a n s i o n n o r m a l t o t h i s p l a n e than p a r a l l e l t o it. F r a c t u r e p l a n e s f o l l o w e d h i g h s o l u t e l a y e r s in b a n d e d s t e e l but o n l y r a r e l y i f e v e r did t h e f i n e b u b b l e s f o r m on i n c l u s i o n s . A t 4 5 0 ° C R E M - t r e a t e d s t e e l w a s a t t a c k e d the f a s t e s t a n d A l - k i l l e d s t e e l r e q u i r e d e x p o s u r e s two t o f o u r t i m e s a s l o n g f o r a t t a c k . IT l"lIGH-temperature, high p r e s s u r e hydrogen m a y c a u s e both s u r f a c e decarburization a n d internal dec a r b u r i z a t i o n ( h y d r o g e n a t t a c k ) in s t e e l . H y d r o g e n a t t a c k (HA) o c c u r s a s a r e s u l t of a t o m i c h y d r o g e n d i f f u s i n g into the s t e e l a n d c o m b i n i n g w i t h c a r b o n i n s o l u t i o n t o f o r m m e t h a n e , w h i c h b e c a u s e of i t s i n s o l u b i l i t y i n s t e e l r e m a i n s t r a p p e d i n t e r n a l l y a s bubb l e s . M i c r o s t r u c t u r a l s t u d i e s h a v e s h o w n that i n t h e a d v a n c e d s t a g e s of h y d r o g e n a t t a c k , l a r g e f i s s u r e s a r e a s s o c i a t e d w i t h a r e a s of d e c a r b u r i z a t i o n o n a m e t a l l o g r a p h i c s e c t i o n .2'4 T h e f i s s u r i n g i s c l e a r l y h e t e r o geneous, i.e. although f i s s u r e s o c c u r a l o n g g r a i n b o u n d a r i e s , not a l l g r a i n b o u n d a r i e s h a v e f i s s u r e s . H o w e v e r , l i t t l e h a s b e e n said in t h e l i t e r a t u r e c o n cerning the b a s i c p r o c e s s e s l e a d i n g to the nucleation a n d g r o w t h of m e t h a n e b u b b l e s , the o b v i o u s p r e c u r s o r to f i s s u r e f o r m a t i o n . I n o t h e r w o r d s , what c h a n g e s o c c u r d u r i n g t h e i n c u b a t i o n p e r i o d to p r o m o t e fiss u r e f o r m a t i o n a n d u l t i m a t e f a i l u r e o f the m a t e r i a l ? Shewmon has analyzed the nucleation and growth
Data Loading...
