Effects of initial microstructure and shock method on the shock-induced transformation strengthening of carbon steels
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R. P. JEWETT,
W. T. CHANDLER,
AND
on
T. E. SCOTT
SAE 1020, 1040, and 1095 s t e e l s w e r e s h o c k - l o a d e d to 158 and 283 k b a r peak p r e s s u r e s by the m o u s e t r a p f l y e r plate technique. P o s t - s h o c k m e c h a n i c a l p r o p e r t i e s , o p t i cal m i c r o s c o p y , and c o m p a r i s o n with data f r o m the l i t e r a t u r e i n d i c a t e d that shock p r e s s u r e duration i s c r i t i cal to s t r e n g t h e n i n g by the ~ ~ ~ p r e s s u r e i n d u ced t r a n s f o r m a t i o n . It is s u g g e s t e d that the c r i t i c a l p r e s s u r e duration is r e l a t e d to a t i m e r e q u i r e d f o r c o m p l e t i o n of the t r a n s f o r m a t i o n p r o c e s s and that the r e q u i r e d duration is i n v e r s e l y dependent on the v o l u m e p e r c e n t c a r b i d e p r e s e n t in the s t e e l .
s types of shock loading t e c h n i q u e s have b e e n e m ployed to i n v e s t i g a t e the e f f e c t of initial m i c r o s t r u c t u r e a n d / o r c h e m i c a l c o m p o s i t i o n on the shock h a r d e n ing r e s p o n s e of s t e e l s , t-5 In one of the m e t h o d s , ~, s a f l y e r plate is a c c e l e r a t e d by an e x p l o s i v e . On i m p a c t the f l y e r plate p r o d u c e s a plane s h o c k wave in the s p e c i m e n . The o t h e r method 2- 4 e m p l o y s an e x p l o s i v e l e n s which c o n v e r t s a point detonation at the a p e x into a plane shock w a v e which u s u a ll y p a s s e s through an a t t e n u a t o r and an a i r gap into the s a m p l e . Shock p r e s s u r e p u l s e s a r e g e n e r a t e d by both t e c h n i q u e s ; h o w e v e r , the e x p l o s i v e l e n s m e t h o d n o r m a l l y g e n e r a t e s p r e s s u r e s of l o n g e r d u r a t i o n . Zukas and F o w l e r , 2 and M in s h a ll , 3 and L o r e e et a l . a all used s i m i l a r a r r a n g e m e n t s in the e x p l o s i v e l e n s technique. Zukas and F o w l e r 2 using p o s t - m o r t e m (after shock was c o m p l e t e d ) o b s e r v a t i o n s found that a s quenched plain c a r b o n s t e e l s with 0.25, 0.45, 0.65, and 1.0 wt pct C did not twin s i g n i f i c a n t l y when s h o c k loaded. F o r all but the 0.25 wt pct C s t e e l , t e m p e r i n g for 24 h r at 700~ was n e c e s s a r y f o r s h o c k - i n d u c e d twinning to o c c u r . They noted that the " i n t e r a c t i o n zone w i d t h " 2 i n c r e a s e d as the h e a t - t r e a t e d condition a p p r o a c h e d the a s - q u e n c h e d s t a t e in s e v e r i t y and a l s o that it i n c r e a s e d l i n e a r l y with c a r b o n content f r o m A r m c o i r o n to 1.0 wt pct C. T h e y a l s o showed that c e m e n t i t e tended to d i s c o u r a g e twin f o r m a t i o n . M i n s h a l P r e p o r t e d that the Hugoniot e l a s t i c l i m i t i n c r e a s e d f r o m 6.8 kbar to 14.8 k b a r and the ~ - t r a n s f o r m a t i o n p r e s s u r e i n c r e a s e d f r o
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