Effect of prestressing on the stress-corrosion resistance of two high-strength steels
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that the p r e s e n c e of c a r b o n a t o m s p r o v i d e s a s t r o n g e r bond b e t w e e n c h r o m i u m a t o m s and d i s l o c a t i o n s than is obtained by d i r e c t i n t e r a c t i o n a s o b s e r v e d in F e - M n N alloys.ll Another possible interaction between chrom i u m a t o m s and d i s l o c a t i o n s is the " m o d u l u s i n t e r a c t i o n " . T h i s i n t e r a c t i o n is known to be r e s p o n s i b l e for so l i d s o l u t i o n h a r d e n i n g in m a n y a l l o y s y s t e m s 12 and could a l s o be r e s p o n s i b l e f o r the j e r k y flow obs e r v e d in the C o - N i - C r - C a l l o y s . The a u t h o r w i s h e s to thank D r . D. J . Lloyd of the M e t a l l u r g i c a l S c i e n c e s L a b o r a t o r y , U n i v e r s i t y of Manitoba f o r m a n y u s e f u l d i s c u s s i o n s , the National R e s e a r c h C o u n c i l of C a n a d a , and the C e n t r e d ' I n f o r m a t i o n du Co b al t , B r u s s e l s , B e l g i u m , f o r f i n a n c i a l support.
Effect of Prestressing on the Stress-Corrosion Resistance of Two
S i n g l e - e d g e notch s p e c i m e n s (1.0 in. wide, 0.5 in. thick) w e r e m a c h i n e d in the t r a n s v e r s e d i r e c t i o n f r o m both s t e e l s . C h a r p y s p e c i m e n s , 0.394 in. sq, w e r e a l s o m a c h i n e d f r o m the m a r a g i n g s t e e l . A l l s p e c i m e n s w e r e f at i g u e p r e c r a c k e d . F a t i g u e c r a c k s a p p r o x i m a t e l y 0.1 in. and 0.03 to 0.05 in. long w e r e p r o d u c e d at the notch r o o t s in the 1 in. wide and Charpy s p e c i mens respectively. P l a n e - s t r a i n fracture toughness KIC tests were conducted on both s t e e l s by t h r e e - p o i n t bending the 1.0 in. wide s p e c i m e n s at r o o m t e m p e r a t u r e a c c o r d i n g to the r e c o m m e n d e d ASTM p r o c e d u r e . 3 R e s u l t s a r e shown in T a b l e II, and i n d i c a t e the s p e c i m e n t h i c k n e s s e s w e r e s u f f i c i e n t to m a i n t a i n plane s t r a i n c o n d i tions f o r the s t r e s s c o r r o s i o n t e s t s . Specimens for s t r e s s - c o r r o s i o n testing were first loaded by t h r e e - p o i n t bending in l a b o r a t o r y a i r , to p r e s t r e s s the c r a c k tip to s e l e c t e d p e r c e n t a g e s (0 to 90 pct) of K I C . The p r e s t r e s s s t r e s s i n t e n s i t y is d e s i g n a t e d a s K i p . Th e load, d e t e r m i n e d f r o m the equation g i v e n by B r o w n and S r a w l e y , 4 was m a i n t a i n e d f o r 30 s e c and then r e m o v e d . No c r a c k g r o w t h o c curred during preloading. All specimens were aged at r o o m t e m p e r a t u r e f o r at l e a s t 24 hr p r i o r to s t r e s s corrosion testing. To e v a l u a t e s t r e s s - c o r r o s i o n r e s i s t a n c e , the p r e s t r e s s e d s i n g l e - e d g e - n o t c h e d s p e c i m e n s w e r e loaded to s e l e c t e d i n i t i a l s t r e s s i n t
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