The effect of aging and cold working on the high-temperature low-cycle fatigue behavior of alloy 800H: Part I. The effec
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I. INTRODUCTION
II. E X P E R I M E N T A L PROCEDURE
ALLOY800H is
an a u s t e n i t i c s t e e l that is widely used by the n u c l e a r i n d u s t r y ; for example, many of the s t e a m - g e n e r a t o r c o m p o n e n t s in G e n e r a l A t o m i c ' s h i g h - t e m p e r a t u r e g a s - c o o l e d r e a c t o r (HTGR) a r e made of 800H. It is t h e r e f o r e not s u r p r i s i n g that c o n s i d e r able r e s e a r c h effort has b e e n d i r e c t e d toward u n d e r s t a n d i n g the influence of the m o r e i m p o r t a n t m e t a l l u r g i c a l v a r i a b l e s on the m i c r o s t r u c t u r e and the m e c h a n i c a l b e h a v i o r of this alloy (see for e x a m p l e R e f s . 1 to 5). In this work, the effect of h a r d e n i n g p r o c e s s e s on the l o w - c y c l e fatigue p r o p e r t i e s of 800H in the t e m p e r a t u r e r a n g e 538 to 760~ is e x a m i n e d . The h a r d e n ing p r o c e s s e s that were c o n s i d e r e d , both i n d i v i d u a l l y and c o l l e c t i v e l y , were p r e c i p i t a t i o n and cold d e f o r m a tion. The l a t t e r m e c h a n i s m is i m p o r t a n t b e c a u s e s o m e cold d e f o r m a t i o n is a l m o s t unavoidable in any fabrication process. M e c h a n i c a l p r o p e r t i e s w e r e studied d u r i n g s t r a i n c o n t r o l l e d l o w - c y c l e fatigue t e s t i n g in e q u i p m e n t which allowed m e a s u r e m e n t of the s t r e s s - s t r a i n c u r v e , and thus the y i e l d s t r e s s and w o r k - h a r d e n i n g r a t e , d u r ing each loading cycle. The effect of the v a r i o u s h a r d e n i n g p r o c e s s e s on these p r o p e r t i e s was d e t e r m i n e d by t e s t i n g s p e c i m e n s that had undergone v a r i ous a m o u n t s of aging and cold working. T h e s e m e c h a n i c a l p r o p e r t i e s were then r e l a t e d to the m i c r o s t r u c t u r e , which was d e t e r m i n e d by X - r a y d i f f r a c t i o n and t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y and d i f f r a c t i o n . P a r t I of this p a p e r will d e a l with the effect of p r e c i p i t a t i o n and cold w o r k on the i n i t i a l s t r e s s - s t r a i n c u r v e of the m a t e r i a l , P a r t II will deal with the effect of these p r o c e s s e s on the b e h a v i o r of the m a t e r i a l d u r i n g s u b s e q u e n t cyclic loading, while P a r t HI will deal with the effects on the b e h a v i o r d u r i n g cyclic loading with the s u p e r p o s i t i o n of c o n s t a n t - s t r a i n hold periods. R. E. VILLAGRANAis Staff Scientist, J. L. KAAE is Senior Technical Advisor, and P. K. GANTZEL is Staff Scientist at General Atomic Company, San Diego, CA 92138. J. R. ELLIS is a Member of the Technical Staff at Oak Ridge National Laboratory, Oak Ridge, TN 37831. Manuscript submitted October 14, 1977. METALLURGICALTRANSACTIONSA
2.1. M a t e r i a l The s p e c i m e n s used in this study were obtained f r o m
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