Kinetics of hydrogen attack and service behavior of steels
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Fig. 4-Optical micrographs of Zr 8.9 pct A1 alloys roiled to strip at 1375 K and transformed to Zr3A1 (matrix) at 1160 K for 30 h: (a) ~600 ppm Fe; 2 • 1 pet (by volume) Zr2AI and 2 • 1 p c t a Zr (AlL (b) ~100 ppm Fe; ~Z0.1 pct Zr2A1 andS0.1 pct(~ Zr (A1). The surface was prepared by anodic color etching; the Zr2A1 phase appeared yellow {light) and rimless, and the a Zr (A1) phase, blue {light or dark) and rimmed by a dark edge.
n e i t h e r i r o n nor o t h e r i m p u r i t i e s could be d e t e c t e d in the a - Z r phase. This point was e s t a b l i s h e d by f r a c t u r i n g the Z r 8.6 pct A1 alloy of p a r a g r a p h one at 77 K9 to exp o s e the a - Z r p a r t i c l e s r e s i d e n t at the g r a i n b o u n d a r i e s , and then a n a l y z i n g the e x p o s e d p a r t i c l e s . In a s e p a r a t e p a p e r , it will be shown that Zr2A1 plays a m a j o r r o l e in the f r a c t u r e of Z r 3 A l - b a s e a l loys. Its c o n t r o l , t h e r e f o r e , is of c o n s i d e r a b l e i m p o r t a n c e . F r o m t h e s e o b s e r v a t i o n s , it follows that a n e c e s s a r y step in obtaining a l l o y s low in Zr2A1 is to r e s t r i c t the i r o n content to 7100 ppm. It a l s o follows
Kinetics of Hydrogen Attack and Service Behavior of Steels F. H~ VITOVEC The p r o p e r t i e s of c a r b o n and low alloy s t e e l s m a y d e t e r i o r a t e when e x p o s e d f o r a p e r i o d of t i m e to p r e s s u r i z e d h y d r o g e n at e l e v a t e d t e m p e r a t u r e . It is well e s t a b l i s h e d that within a c e r t a i n t e m p e r a t u r e r a n g e , this d a m a g e is c a u s e d by a r e a c t i o n of h y d r o g e n with the c a r b o n of the s t e e l to f o r m m e t h a n e . At high t e m p e r a t u r e and low h y d r o g e n p r e s s u r e , the r e a c t i o n may o c c u r e n t i r e l y at the s u r f a c e and w e a k e n the s t e e l by progressive surface decarburization. Increased hydrogen p r e s s u r e s shift the r e a c t i o n to i n t e r n a l s u r f a c e s such as g r a i n b o u n d a r i e s o r i n c l u s i o n - s t e e l i n t e r f a c e s . The l o c a l i z e d i n t e r n a l d e c a r b u r i z a t i o n and the build up of m e t h a n e p r e s s u r e r e s u l t s in f i s s u r e s which induce
F. H. VITOVEC is Professor of Metallurgical Engineering, Department of Mineral Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 2G6. Manuscript submitted May 24, 1977. METALLURGICAL TRANSACTIONS A
that i r o n - p r o b i n g is a p r a c t i c a l m e a n s f o r d e t e c t i n g Zr2A1 on f r a c t u r e s u r f a c e s 9 T h e a u t h o r s a c k n o w l e d g e the t e c h n i c a l a s s i s t a n c e of J , B a i r d , J . A. Roy, and T . P. T r o t t i e r , and thank B . J . S . Wilkins f o r the a l l o y s .
1 E.M. Schulson and D. B. Graham"ActaMet, 1976, vol. 24, p. 615. 2. M. Gagn4and E M. Schulson Met. Trans. A, 1976,vol 7A, p.
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