Plastic deformation of austenitic iron at intermediate strain rates
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ALTHOUGH
t h e r e have been n u m e r o u s i n v e s t i g a t i o n s of the m e c h a n i c a l b e h a v i o r of a u s t e n i t i c i r o n and l o w c a r b o n s t e e l s , a c o m p l e t e l y a d e q u a t e r e p o r t of the t e n s i l e d e f o r m a t i o n o v e r the e n t i r e t e m p e r a t u r e r a n g e 910 to 1400~ (0.65 to 0.92 T m ) is not a v a i l a b l e . F o r e x a m p l e , of twenty -one known i n v e s t i g a t i o n s of the m e c h a n i c a l b e h a v i o r at t e m p e r a t u r e s above 1000~ ~-2~ only ten ~'s'4' 6, 9, ~o, ~3, ~, ~7, 2~ extend to t e m p e r a t u r e s above 1200~ s e e Table I. F o r t h r e e of t h e s e ten i n v e s t i g a tions the loading mode was t o r s i o n , which has the d i s advantage in s o l i d b a r s of c o m p l e x s t r e s s d i s t r i b u t i o n s s o that the r e s u l t s obtained cannot be s i m p l y i n t e r p r e t e d . Of the r e m a i n i n g s e v e n i n v e s t i g a t i o n s , a d a m aging o x i d i z i n g a t m o s p h e r e was u s e d in three.~'4'6 T h r e e o t h e r i n v e s t i g a t i o n s 3'~3'~7 i n v o l v e d c o n s t a n t s t r e s s o r c o n s t a n t - f o r c e m o d e s of loading, and only m i n i m u m s t r a i n r a t e s w e r e noted, l e a v i n g the t r a n s i e n t d e f o r m a t i o n b e h a v i o r u n r e c o r d e d e x c e p t f o r one s t e e l in Ref. 3. In the final i n v e s t i g a t i o n ~ s t e e p t e m p e r a t u r e g r a d i e n t s within the s p e c i m e n m a d e m e a s u r e m e n t of s t r a i n u n c e r t a i n . It was the a b o v e - d e m o n s t r a t e d p a u c i t y of r e l i a b l e m e a s u r e m e n t s of s t r e s s and s t r a i n , o b t a i n e d under c o n t r o l l e d c o n d i t i o n s and o v e r a b r o a d r a n g e of t e m p e r a t u r e , that p r o m p t e d the i n v e s t i g a t i o n d e s c r i b e d in this p a p e r . In addition to the t e m p e r a t u r e of d e f o r m a t i o n , the c o n t r o l l e d v a r i a b l e s w e r e s t r a i n r a t e , a n n e a l i n g t e m p e r a t u r e , and to a l i m i t e d extent, c o m p o sition. The s t r a i n r a t e s e m p l o y e d , 2.8 • 10 -~ to 2.3 x 10 -~ s -~, e x i s t d u r i n g the s o l i d i f i c a t i o n and c o o l i n g of c a s t i n g s as w e l l as in s o m e f o r m i n g o p e r a t i o n s where large strain-rate gradients are present. E X P E R I M E N T A L A P P A R A T U S AND PROCEDURE
z o n e - r e f i n e d i r o n was p r o d u c e d . 22 The c y l i n d r i c a l t e n s i o n s p e c i m e n s w e r e of the b u t t o n - h e a d type with a d i a m e t e r of 3.2 m m , a g a g e - l e n g t h - t o - d i a m e t e r r a t i o of 11.50, and a f i l l e t r a d i u s of 0.25 m m . A c o m m e r c i a l l y a v a i l a b l e v a c u u m f u r n a c e was u s e d to obtain the r e q u i r e d t e m p e r a t u r e s . B e f o r e h e a t i n g , the f u r n a c e c h a m b e r was e v a c u a t e d to about 0.3 m P a (2 •
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