Decarburization kinetics of low alloy ferritic steels in sodium
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J. L. KRANKOTA and J. S. ARMIJO are Engineer and Manager, respectively, Plant Materials and Processes Unit, Breeder Reactor Department, General Electric Co., San Jose, Calif. Manuscript submitted July 6, 1971. METALLURGICAL TRANSACTIONS
II) E X P E R I M E N T A L METHODS A m a j o r p u r p o s e of t h i s i n v e s t i g a t i o n w a s to c o l l e c t 9 . 1 d a t a on the d e c a r b u r l z a t l o n of 2~ C r - 1 Mo t e s t s p e c i m e n s in a f o r m that would p e r m i t p r e d i c t i o n of the d e c a r b u r i z a t i o n of 288 C r - 1 Mo in a b i m e t a l l i c , s o d i u m s y s t e m . It was d e c i d e d that the c o m p l i c a t i n g e f f e c t s of a n o n i s o t h e r m a l , flowing s o d i u m s y s t e m on t h e a n a l y s i s of the c a r b o n t r a n s p o r t p r o c e s s could be a v o i d e d with a pot of s t a t i c s o d i u m . It w a s a l s o d e s i r a b l e to ~ r o d u c e the f a s t e s t p o s s i b l e r a t e of d e c a r b u r i z a t i o n of 2z C r - 1 Mo in o r d e r to obtain a c o n s e r v a t i v e e s t i m a t e of t h e amount of d e c a r b u r i z a t i o n that would o c c u r in s o d i u m h e a t e d s t e a m g e n e r a t o r s d u r i n g s e r v i c e life. A) E q u i p m e n t Since the flux of c a r b o n out of 2~ C r - 1 Mo i s d i r e c t l y p r o p o r t i o n a l to the c a r b o n a c t i v i t y g r a d i e n t in the s y s t e m , the c a r b o n a c t i v i t y w a s fixed at a v e r y low l e v e l . T h i s w a s done by p l a c i n g t i t a n i u m sponge with a l a r g e s u r f a c e a r e a in the s o d i u m . The t e s t v e s s e l c o n t a i n i n g the s o d i u m , t i t a n i u m sponge, and s t a i n l e s s s t e e l c a g e i s shown in F i g . 1. D e t a i l s of the s y s t e m p a r a m e t e r s a r e l i s t e d in T a b l e I. S a m p l e s w e r e r e t r i e v e d f r o m the v e s s e l a f t e r the s o d i u m w a s d r a i n e d into a dump tank and the s a m p l e s w e r e r a p i d l y r e m o v e d in a i r a t r o o m t e m p e r a t u r e . A d e s c r i p t i o n of the m a t e r i a l s and g e o m e t r y of s p e c i m e n s e x p o s e d in the t e s t v e s s e l i s given in T a b l e H. T h e s a m p l e s w e r e w i r e d t o g e t h e r in a s t r i n g and p l a c e d in the a n n u l u s b e t w e e n the c a g e s that c o n t a i n e d the t i t a n i u m sponge, F i g . 1. B) T e s t P r o c e d u r e The s a m p l e s w e r e c l e a n e d , w e i g h e d and a r r a n g e d in s i x s t r i n g s , e a c h s t r i n g c o n t a i n i n g t h e s a m e t y p e of VOLUME 3, SEPTEMBER 1972-2515
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Table I. System Parameters
I
Volume of sodmm- 12.0 1 Volume of cover gas, argon-3.3 1 Cover gas pressure-5 psig, argon Titanium sponge surface area- 12.100 cm2 weight-7250 g Stainless steel cage, type 304 SS surface area-34,200 cm2 wetght-2970 g Stainlesssteel vessel,type 304 SS surface area-3900 cm2 wetght-25,850 g Carbon steel specimens* surface area-4250 cm: weight-6900 g
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