Note on the metallurgy of Fe-Cr-Al alloys
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i n s e r t e d ) in the c e n t e r of a m i l d s t e e l p l at e of the s a m e t h i c k n e s s . 6 T h e c o m p o s i t e s w e r e r e h e a t e d to 760~ and r e d u c e d d i r e c t l y in two p a s s e s to n o m i n a l 0.045 in. t h i c k n e s s . T h u s , e a c h a l l o y w as e l o n g a t e d to a s t r i p of about 12 in. l e n g t h • 1.5 in. width, with t a p e r e d en d s, w h i ch p r o v i d e d si x t e n s i l e t e s t s p e c i m e n s having a g a g e s e c t i o n of 0.25 in. width x 1.0 in. l e n g t h (6.35 • 25 ram). T h e s e t e n s i l e t e s t s p e c i m e n s w e r e g i v e n a s o l u t i o n t r e a t m e n t of 0.5 h at 870 o r 1000~ and w a t e r q u e n c h e d . A s s e e n in T a b l e II, the five s h e e t a l l o y s q u e n c h e d f r o m 870~ p r o d u c e d 66 to 87,000 p s i (455 to 600 M P a ) yield s t r e n g t h , 80 to 105,000 p s i (552 to 724 M P a ) u l t i m a t e s t r e n g t h with 24 to 18 pct e l o n g a t i o n . T h e s p e c i m e n s q u e n c h e d f r o m 1000~ p r o d u c e d 58 to 79,200 p s i (400 to 545 M P a ) y i e l d s t r e n g t h and 77,600 to 103,500 p s i (535 to 713 M P a ) u l t i m a t e s t r e n g t h w i t h 32 t o 21 pct e l o n g a t i o n . In both c a s e s , the i n c r e a s e in s t r e n g t h and d e c r e a s e in d u c t i l i t y w as p r o d u c e d by t he i n c r e a s e in t i t a n i u m c o n t e n t . An i m p o r t a n t a s p e c t in c o m p a r i n g t h e s e two s e t s of d a t a is the f a c t t h a t the 1000~ a n n e a l i n g t r e a t m e n t did not e m b r i t t l e t h e s e a l loys but did p r o d u c e l o w e r s t r e n g t h p r o p e r t i e s than a n n e a l i n g at 870~ M a i n t a i n i n g t e n s i l e d u c t i l i t y at the s a m e l e v e l c a n be a t t r i b u t e d to the low i n t e r s t i t i a l c o n t e n t and p o s s i b l y the a b s e n c e of s i l i c o n in t h e p r e s e n c e of t i t a n i u m . Th e o p t i c a l m i c r o s t r u c t u r e was s i n g l e p h a s e f e r r i t e with minute p a r t i c l e s that w e r e d i s t r i b u t e d within c e r t a i n g r a i n s . Th e g r a i n s i z e was A S T M 7 in the s p e c i m e n s that w e r e q u e n c h e d f r o m 870~ and A S T M 5 and 6 in t h o s e that w e r e q u e n c h e d f r o m 1000~ Grain c o a r s e n i n g did not o c c u r at the l a t t e r t e m p e r a t u r e with the a d d i t i o n of 0.TTi. SEM v i e w s of the t e n s i l e f r a c t u r e s showed a t r a n s g r a n u l a r d i m p l e d s u r f a c e c a u s e d by m i c r o v o i d c o a l e s c e n c e f o r both t r e a t m e n t s .
Table I. Composition of Experimental Alloys, Wt Pet
Heat A B c D E
Cr 64 7.1 7.8 78 6.4
A1
Cu
Tl
5.5 5.4 5.4 5.3 5.4
0.7 0.7 0.7 0.7 14
0.7 14 2.0 2.8 1.4
Alloyscontain 0.013C and 0.0025N
Table II. Tensile Test Results on Fe-Cr-AI Sheet Alloys
Heat A B c D E A B C D E
0 2 Pct Yxeld Ultimate Ksi MPa Ksi MPa 870~ for 0.5 h and Quenched 455 79.5 548 66.0 77.4 534 88.8 6
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