Heat treatment effects on creep and rupture behavior of annealed 2.25 Cr-1 Mo steel
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A N N E A L E D 2 1/4 Cr-1 Mo s t e e l is b e i n g c o n s i d e r e d a s s t r u c t u r a l m a t e r i a l for the s t e a m g e n e r a t o r s of B r e e d e r R e a c t o r s . It is also in c o m m o n use in f o s s i l fueled power g e n e r a t i o n s y s t e m s . Two types of a n n e a l i n g t r e a t m e n t s a r e c o m m o n l y used for this s t e e l : 1'2 a full a n n e a l and an i s o t h e r m a l a n n e a l . Both heat t r e a t m e n t s give a m i c r o s t r u c t u r e that is p r i m a r i l y p r o e u t e c t o i d f e r r i t e . P r e v i o u s l y we i n v e s t i gated the effect of heat t r e a t m e n t on t e n s i l e p r o p e r t i e s , and a definite effect was o b s e r v e d . ~ The objective of this study was an i n v e s t i g a t i o n of the effect of the a n n e a l i n g t r e a t m e n t on the c r e e p and c r e e p - r u p t u r e properties. EXPERIMENTAL T h r e e s e c t i o n s of a 25 m m thick s t e e l plate taken f r o m a single heat (B and W 20017) were t e s t e d (Table I). Two s e c t i o n s were given d i f f e r e n t full a n n e a l s (diff e r e n t f u r n a c e cooling r a t e s ) and one was given an i s o t h e r m a l a n n e a l . The fully a n n e a l e d s e c t i o n s were a u s t e n i t i z e d 1 h at 927~ and then f u r n a c e cooled at different r a t e s . The other s e c t i o n was i s o t h e r m a l l y a n n e a l e d by f u r n a c e cooling f r o m 927 to 704~ at about 83~ holding at that t e m p e r a t u r e for 2 h, then f u r nace cooling (Fig. 1). F o r c o m p a r i s o n , the curve for the a i r - c o o l e d plate ( n o r m a l i z e d ) i s a l s o shown in Fig, 1. H e r e a f t e r , the two a n n e a l e d plates will be r e f e r r e d to a s AN- 1 and AN- 2 (AN- 2 was cooled f a s t e r than A N - l ) , and the i s o t h e r m a l l y a n n e a l e d plate as IA. Most of our t e s t s were made on AN-1 and IA. The m i c r o s t r u c t u r e s of the s t e e l in these t h r e e h e a t - t r e a t e d conditions were p r e v i o u s l y d i s c u s s e d . I A f t e r all t h r e e heat t r e a t m e n t s , the m i c r o s t r u c t u r e s were p r i m a r i l y p r o e u t e c t o i d f e r r i t e with s o m e p e a r -
Table I. Chemical Composition of 25 mm Plate of Annealed 2 1/4 Cr-1 Mo Steel
Analysis Vendor ORNL
C
Mn
ChemicalComposition,WtPct Si Cr Mo Ni
0.11 0.55 0.29 0.135 0.57 0.37
2.13 2.2
0.90 0.92
0.16
S
P
0.014 0.016
0.01 ] 0.012
life and b a i n i t e . Heat t r e a t m e n t s AN-1, AN-2, and IA were e s t i m a t e d to have r e s p e c t i v e l y 20, 25, and 20 pct b a i n i t e and 1, < 1, and 1 pct p e a r l i t e . F o r the c o n s t a n t - l o a d c r e e p - r u p t u r e t e s t s at 454, 510, and 566~ s p e c i m e n s with a 6.4 m m d i a m • 63.5 m m long r e d u c e d s e c t i o n were used. The t e s t s were made in a i r on constant load l e v e r - a r m c r e e p f r a m e s with 12/1 and 20/1 r a t i o s ; the s p e c i m e n s were heated by a M a
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