Thermal recovery in 304 stainless steel following explosive shock loading and explosive forming
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E X P E R I M E N T A L PROCEDURE Rolled and a n n e a l e d (0.25 h r at 1060~ sheet s a m ples of 304 s t a i n l e s s s t e e l in the f o r m of 1 in. 2 plates 0.007 in. thick w e r e shock-loaded to p r e s s u r e s of 150, 4 2 5 , 7 5 0 , and 1200 k b a r a s p r e v i o u s l y d e s c r i b e d . ~'4' s S e a m l e s s 304 s t a i n l e s s s t e e l c y l i n d r i c a l tubing s a m p l e s of v a r y i n g d i a m e t e r , a n o m i n a l wall t h i c k n e s s of 0.0055 in., and length of 5.55 in., w e r e e x p l o s i v e l y expanded 0.5, 9, 25, 32, and 62 pct u s i n g a c o n s t r a i n t s y s t e m and s h o c k - l o a d i n g a s s e m b l y p r e v i o u s l y d e s c r i b e d by Foltz et al.6 The n o m i n a l c o m p o s i t i o n s of the sheet and tubing s a m p l e s a r e shown in T a b l e I, and the g r a i n size for both m a t e r i a l s was a p p r o x i m a t e l y 15~. The pulse duration for the explosive shock-loading experiments was maintained constant at 2 p sec. The strain rates for the explosively expanded cylinders was 4 1 2 measured to range from 1 to 4 x 10 sec- . Specimens for transmission electron microscopy were prepared from annealed sections of the shockloaded sheets and the expanded cylinder walls using the technique described by Murr.7 The cylindrical samples were originally extracted from the expanded tubes by cutting them open and pulling them reasonably flat. Test samples measuring 0.25 in. in width for each tubing and for each shock-loaded sheet material, were placed along with smaller samples measuring about 0.2 in.2 for microhardness measurements into quartz tubes evacuated (at 10-5 torr), and sealed for furnace a n n e a l s of 1 h r at t e m p e r a t u r e s of 700 ~ 800 ~ and 900~ These temperatures were determined from p r e v i o u s 0.10 h r h a r d n e s s r e c o v e r y c u r v e s for 750
Table I. Sample Composition, wt pct Fe
304 Stainless Sheet 304 Stainless Steel Tubing Steel
70.39
Ni
Cr
Cu
9.52 18.43 0.14
69.55 9.75
18.41
-
S
Mn
Si
C
-
1.05
0.03
1.70 0.50 0.06
0.42 0.06
VOLUME 1,DECEMBER 1970-3333
and 1200 k b a r shock-loaded s t a i n l e s s steel to r e p r e sent the a p p r o x i m a t e r a n g e of p r o b a b l e s u b s t r u c t u r a l r e c o v e r y . The t r a n s m i s s i o n s p e c i m e n s from s a m p l e s a n n e a l e d at 700 ~ 800 ~ and 900~ w e r e o b s e r v e d in a Hitachi P e r k i n - E l m e r 125 e l e c t r o n m i c r o s c o p e o p e r ated at 125 key, employing a g o n i o m e t e r tilt stage. The a n n e a l i n g k i n e t i c s w e r e d e t e r m i n e d by V i c k e r s m i c r o h a r d n e s s m e a s u r e m e n t s u s i n g a 100 g load on r e p r e s e n t a t i v e s p e c i m e n s for e a c h a n n e a l i n g condition. M i c r o h a r d n e s s s a m p l e s m e a s u r i n g a p p r o x i m a t e l y 0.2 in. 2 w e r e cut from each of the s h o c k - l o a d e d and explos i v e l y expanded m a t e r i a l s and s e a l e d in quartz tubes evacuated to roughl
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