Effect of residual elements on radiation strengthening in iron alloys, pressure vessel steels, and welds
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N E of the m a j o r f a c t o r s of c o n c e r n in the r e l i a b i l i t y of p r e s s u r e v e s s e l s t e e l s for n u c l e a r s e r v i c e is the i n c r e a s e in b r i t t l e to ductile t r a n s i t i o n t e m p e r a t u r e , or e m b r i t t l e m e n t , which r e s u l t s f r o m e x p o s u r e to n e u t r o n i r r a d i a t i o n . 1 An e x t e n s i v e p r o g r a m over the past six y e a r s has been in p r o g r e s s at the Naval R e s e a r c h L a b o r a t o r y (NRL) to c h a r a c t e r i z e the f a c t o r s i n f l u e n c i n g e m b r i t t l e m e n t . This r e s e a r c h led to the c o r r e l a t i o n of the r e s i d u a l e l e m e n t s , copper and p h o s p h o r u s , with the d e g r e e of e m b r i t t l e m e n t of p r e s s u r e v e s s e l s t e e l s 2 and w e l d m e n t s 3 i r r a d i a t e d n e a r the t y p i cal s e r v i c e t e m p e r a t u r e for r e a c t o r p r e s s u r e v e s s e l s , 290~ T h i s p r i n c i p l e was s u c c e s s f u l l y t r a n s f e r r e d to c o m m e r c i a l p r a c t i c e with the d e m o n s t r a t i o n that e m b r i t t l e m e n t in a 30 ton heat of A533-B p r e s s u r e v e s s e l s t e e l could be held to o n e - t h i r d that in typical c o m m e r cial heats through close c o n t r o l of the r e s i d u a l e l e m e n t s p e c i f i c a t i o n s .4 In spite of t h e s e c l e a r d e m o n s t r a t i o n s of the i m p o r t a n c e of r e s i d u a l e l e m e n t s in e m b r i t t l e m e n t , the d e t a i l s of the m e c h a n i s m w e r e not evident thus m a k i n g it difficult to g e n e r a l i z e the r e s u l t s to other s t e e l s and a p p l i c a t i o n s . A p r o g r a m to d e t e r m i n e the m e c h a n i s m of e m b r i t t l e m e n t was i n i t i a t e d and the p r e s e n t e x p e r i m e n t s u s i n g c o m p r e s s i o n t e s t i n g a r e p a r t of that effort. An a n a l y s i s ~ of m e c h a n i s m s by which copper might i n fluence the e m b r i t t l e m e n t of p r e s s u r e v e s s e l s t e e l s indicated two m e c h a n i s m s could p l a u s i b l y explain the effect. In one, enhanced diffusion in the high v a c a n c y c o n c e n t r a t i o n a c c o m p a n y i n g i r r a d i a t i o n might lead to s e g r e g a t i o n of copper a n d / o r p h o s p h o r u s at an i n t e r face. This p o s s i b i l i t y was tested by Afiger s p e c t r o scopy a n a l y s i s of f r a c t u r e s u r f a c e s of i r r a d i a t e d p r e s s u r e v e s s e l s t e e l s , 6 and it was found that no s e g r e g a t i o n of copper or p h o s p h o r u s could be detected on F. A. SMIDT, JR. and H. E. WATSONare Heads of the Radiation Damage MechanismsSection and Radiation Operations Section, respectively, Reactor Materials Branch, Naval Research Laboratory (Code 6390), Washington,D. C. Manuscript submitted November 4, 1971. METALLURGICALTRANSACTIONS
the f r a c t u r e s u r f a c e . A second m e c h a n i s m p o s t u l
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