Grain-boundary corrosion of type 304 stainless steel by cesium oxides
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EXPERIMENTAL
a s s e m b l y is e n c a p s u l a t e d in an e v a c u a t e d q u a r t z tube to p r o t e c t a g a i n s t o x i d a t i o n d u r i n g the i s o t h e r m a l t e s t s . I n a s m u c h a s c e s i u m o x i d e s r e a c t with a i r and m o i s t u r e , a l l loading and w e l d i n g o p e r a t i o n s w e r e p e r f o r m e d in a d r y glovebox f i l l e d with an i n e r t gas such a s h e l i u m o r h e l i u m - a r g o n m i x t u r e . The c h e m i c a l a n a l y s i s of T y p e 304 s t a i n l e s s s t e e l i s shown in T a b l e I. T h e c e s i u m oxide u s e d for k i n e t i c s t u d i e s i s of c o m m e r c i a l g r a d e , which p r i n c i p a l l y c o n t a i n s C s 2 0 , and Cs202 and has r e l a t i v e l y s m a l l e r q u a n t i t i e s of Cs203. The p r o c e d u r e c o n s i s t s of m a i n t a i n i n g the s t a i n l e s s s t e e l s p e c i m e n e x p o s e d to c e s i u m o x i d e s at a fixed t e m p e r a t u r e for a p r e d e t e r m i n e d t i m e followed by m e t a l l o g r a p h i c e x a m i n a t i o n of the c r o s s s e c t i o n of the s p e c i m e n and tube. As r e p o r t e d e a r l i e r , 1 the p e n e t r a t i o n of T y p e 304 s t a i n l e s s s t e e l by c e s i u m o x i d e s o c c u r s along the g r a i n b o u n d a r i e s at t e m p e r a t u r e s b e t w e e n 450 ~ and 690~ The p e n e t r a t i o n depth w a s m e a s u r e d on an e n l a r g e d i m a g e with a c a l i b r a t e d e y e p i e c e . The depth of p e n e t r a t i o n was m e a s u r e d a r o u n d the c i r c u m f e r e n c e n o r m a l to the s u r f a c e e x p o s e d to liquid o r s o l i d c e s i u m o x i d e s , and an a v e r a g e v a l u e of the p e n e t r a t i o n depth was u s e d to define the e x t e n t of c o r r o s i o n . An e x a m p l e of g r a i n - b o u n d a r y p e n e t r a t i o n
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END CAP TIG WELD
STAINLESS STEEL TUBE
PROCEDURE
The capsule used for the study of grain-boundary corrosion of stainless steel by cesium oxides is shown in Fig. I. A stainless steel specimen (0.175 in. diam by 0.735 in. long) is placed in contact with cesium oxides in a stainless steel tube (0.29 in. OD by 0.25 in. ID by 2.5 in. long) of the same composition. The entire P. S. MAIYA and D. E. BUSCH are Metallurgist and Senior Technician, respectively, Materials Science Division, Argonne National Laboratory, Argonne, 111.60439. Manuscript submitted August 30, 1972. METALLURGICAL TRANSACTIONS
--CESIUM
OXIDE
STAINLESS STEEL SPECIMEN
WELD END CAP
Fig. 1--Experimental arrangement for cesium oxide-stainless steel corrosion tests. VOLUME 4, MARCH 1973 663
Table I. Chemical Analysis of Type 304 Stainless Steal
Element
Table II. Linear Rate Constants for the Reaction Between Cesium Oxides and Stainless Steel at Various Temperatures
Analysis, Wt Pct
Cr Ni Mn Si Ta C P S O Fe
18.67 10.1 1.28 0.59
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