Hydrogen assisted cracking of sensitized 304 stainless steel
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Table I, Chemical Composition of 304 Stainless
Hydrogen Assisted Cracking of Sensitized 304 Stainless Steel
Ni
Cr
Mn
C
N
S
Si
P
Cu
8.49
18.1
1.12
0.078
0.05
0.027
0.41
0.025
0.21
C. L. BRIANT In r e c e n t y e a r s t h e r e have b e e n m a n y s t u d i e s of hydrogen a s s i s t e d c r a c k i n g in s t a i n l e s s s t e e l s , a-~~ T h i s work has e x a m i n e d both f e r r i t i c and 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 and has shown that m a n y of these a r e s u s c e p t i b l e to h y d r o g e n c r a c k i n g . One q u e s t i o n which has not b e e n a n s w e r e d s a t i s f a c t o r i l y is whether o r not h y d r o g e n c r a c k i n g m a y be a n i m p o r t a n t p r o c e s s in what a r e r e p o r t e d to be c o r r o s i o n or s t r e s s c o r rosion failures. In this note we a d d r e s s this p r o b l e m . Hydrogen c r a c k i n g has b e e n e x a m i n e d in a c o m m e r c i a l heat of 304 s t a i n l e s s s t e e l heat t r e a t e d to two d i f f e r e n t cond i t i o n s . In one of t h e s e c o n d i t i o n s the s a m p l e s were v e r y s u s c e p t i b l e to i n t e r g r a n u l a r c o r r o s i o n ( s e n s i tized); in the other they were c o m p l e t e l y i m m u n e to c o r r o s i o n ( u n s e n s i t i z e d ) . Since hydrogen is a b y - p r o duct of m a n y c o r r o s i o n r e a c t i o n s , one can hypothes i z e that it might play a p a r t in many f a i l u r e s of s t a i n l e s s s t e e l o t h e r w i s e a t t r i b u t e d to c o r r o s i o n o r s t r e s s c o r r o s i o n . T h i s idea would gain s u p p o r t if corrosion sensitized samples fractured more easily in h y d r o g e n than u n s e n s i t i z e d s a m p l e s , and, in p a r t i c u l a r , if the h y d r o g e n f r a c t u r e mode is i n t e r g r a n u l a r in the s e n s i t i z e d and t r a n s g r a n u l a r in the u n s e n s i t i z e d s a m p l e s . A s the p r e s e n t r e s u l t s will show, the b e havior of s e n s i t i z e d and u n s e n s i t i z e d 304 s t a i n l e s s s t e e l in hydrogen p a r a l l e l s that found in c o r r o s i v e environments. A l l s a m p l e s w e r e i n i t i a l l y solution a n n e a l e d at 1373 K for 1 h and then w a t e r quenched. A f t e r this t r e a t m e n t the s a m p l e s were in the u n s e n s i t i z e d condition. To a c h i e v e s e n s i t i z a t i o n , s a m p l e s were then a n n e a l e d at 923 K for 24 h. To cheek that these heat t r e a t m e n t s did p r o d u c e m a t e r i a l with d i f f e r e n t c o r r o s i o n s u s c e p t i b i l i t i e s , s a m p l e s of each w e r e s u b j e c t e d to a modified 72 h S t r a u s s t e s t . n The s e n s i t i z e d s a m pies w e r e c o r r o d e d to the extent that they could e a s i l y be f r a c t u r e d by hand. T h e s e f r a c t u r e s w e r e c o m p l e t e l y i n t e r g r a n u l a r . The u n s e n s i t i z e d s a m p l e s w e r e not attacked. The c
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