Microstructural stability of thermal-mechanically pretreated type 316 austenitic stainless steel
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beneficial in improving the p o s t i r r a d i a t i o n ductility of austenitic s t a i n l e s s s t e e l , ta Unfortunately, not a g r e a t deal is known about the m i c r o s t r u c t u r a l s t a b i l i t y of v a r i o u s austenitic s t a i n l e s s s t e e l s as a function of t h e r m a l and mechanical p r e t r e a t m e n t s which v a r y such potentially i m p o r t a n t p a r a m e t e r s as dislocation density, g r a i n size, alloying e l e m e n t s in solution, p r e c i p i t a t e d i s t r i b u t i o n and size, p r e c i p i t a t e morphology, and so forth. The p r e s e n t r e s e a r c h was undertaken in an effort to r e m e d y this s i t uation for the case of type 316 s t a i n l e s s s t e e l . I) SCOPE OF THE PRESENT RESEARCH In the work r e p o r t e d h e r e we have investigated the r e c o v e r y and r e c r y s t a l l i z a t i o n behavior and the phase s t a b i l i t y of type 316 austenitic s t a i n l e s s s t e e l in a f a i r l y r e s t r i c t e d t e m p e r a t u r e range but with a r e l a t i v e l y wide range of p r e t r e a t m e n t s . Aging t r e a t m e n t s have been c a r r i e d out at 550 ~, 650 ~ and 710~ for a v a r i e t y of t i m e s . The maximum aging t i m e at 650 ~ or 710~ was 3250 h and at 550~ it was 4400 h. A t y p i c a l sequence of aging t i m e s (in hours) might be 1, 4, 24, 168, 1359, and 3250. A few short t e r m t r e a t m e n t s have also been c a r r i e d out at 760~ The p r e t r e a t m e n t s investigated a r e s u m m a r i z e d in Table I. Henceforth, the v a r i o u s p r e t r e a t m e n t s will be r e f e r r e d to by the designations in Table I whenever this is most convenient. F o r example, m a t e r i a l solution t r e a t e d at 1050~ and then r e d u c e d 30 pet will be designated B3. C l e a r l y these p r e t r e a t m e n t s r e p r e s e n t a v e r y wide v a r i e t y of initial conditions. A few c o m ments concerning the v a r i o u s t r e a t m e n t s will help to c l a r i f y the r e a s o n s for the choices made. The A type ( a s - s o l u t i o n t r e a t e d ) was s e l e c t e d in p a r t b e c a u s e there is data in the l i t e r a t u r e on the phase stabilityof solution t r e a t e d austenitic s t a i n l e s s s t e e l s . VOLUME 4, JUNE 1973-1533
Table I. Pretreatment Conditions for Microstructural Stability Studies of Austenitic Stainless Steels
Table II. Chemical Analysis of the Type 316 Austenitic Stainless Steel
Composition, wt. pet. A. Solution treatment at the following temperatures, water quench. 1. 1050~ 2. 1200~ B. Solution treatment at 1050~ plus the following amounts of cold (room temperature) reduction in thickness by rolling. 1. 2. 3. 4.
10 tact 20 ~ t 30 pet 50 pet
C. Production of fine-grained material by repeated cold working and recrystallization. Cold reduced 40 pet, annealed 1 h at 760~ cold reduced 40 pct, annealed 1 h at 760~ cold reduced 50 pet, annealed 2 h at 760~ plus the following amounts of additional cold reduction in thick
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