Effect of strain rate on stress corrosion cracking in duplex type 304 stainless steel weld metal
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Constant s t r a i n - r a t e t e s t s * p e r f o r m e d by T a k a n o ~ *Strain-rate in these tests remains constant prior to crack initiation only if an ideally " h a r d " loading system is employed.
on wholly a u s t e n i t i c 1 9 C r - 1 0 N i a u s t e n i t i c s t a i n l e s s s t e e l s in b o i l i n g 42 pct MgC12 have i n d i c a t e d that t r a n s g r a n u l a r to i n t e r g r a n u l a r s t r e s s - c o r r o s i o n c r a c k ing t r a n s i t i o n s a r e c l o s e l y r e l a t e d to the f o r m a t i o n of s l i p s t e p s and the c o r r o s i o n r a t e of s l i p s t e p s d u r i n g s t r e s s i n g . At low s t r a i n - r a t e s , d i s s o l u t i o n of s l i p s t e p s o c c u r s a l o n g f a v o r a b l y o r i e n t e d s l i p p l a n e s within g r a i n s , and r e s u l t s in a t r a n s g r a n u l a r s t r e s s - c o r r o sion c r a c k i n g m o r p h o l o g y . I n c r e a s i n g the s t r a i n - r a t e c a u s e s a c o r r e s p o n d i n g i n c r e a s e in the r a t e of s l i p s t e p f o r m a t i o n . If s l i p s t e p d i s s o l u t i o n cannot keep pace with s l i p s t e p f o r m a t i o n , d i s l o c a t i o n p i l e - u p s a r e c r e a t e d , and s t r e s s e s i n c r e a s e within the g r a i n s . When the magnitude of t h e s e s t r e s s e s b e c o m e s s u f f i c i e n t l y g r e a t , g r a i n b o u n d a r y p l a s t i c d e f o r m a t i o n o c c u r s and i n t e r g r a n u l a r d i s s o l u t i o n is p r e f e r r e d . T h u s , c h a r a c t e r i s t i c s of the g r a i n b o u n d a r y d e f e c t s t r u c t u r e (e.g., d i s l o c a t i o n d e n s i t y and configuration, v a c a n c y and i m p u r i t y a t o m c o n c e n t r a t i o n s ) a p p a r e n t l y p l a y an i m p o r t a n t r o l e in d e t e r m i n i n g s t r e s s - c o r r o s i o n c r a c k i n g morphology. T r a n s m i s s i o n e l e c t r o n m i c r o s c o p y s t u d i e s conducted on duplex T y p e 304 s t a i n l e s s s t e e l weld m e t a l s have shown that a s e m i c o h e r e n t b o u n d a r y e x i s t s at the a u s t e n i t e - f e r r i t e i n t e r f a c e .a If "interphase- i n t e r f a c e ' ' W. A. BAESLACK III, Lt., USAF, formerly with Rensselaer Polytechnic Institute, Troy, New York, is now with Air Force Materials Laboratory, Wright Patterson AFB, OH 95433. D. J. DUQUETTE and W, F. SAVAGE are Professors of Metalurgical Engineering, Rensselaer Polytechnic Institute, Troy, New York. Manuscript submitted September 1, 1978. METALLURGICAL TRANSACTIONS A
s t r e s s - c o r r o s i o n c r a c k i n g in duplex weld m e t a l s is d e p e n d e n t on the d e f e c t s t r u c t u r e at the b o u n d a r y in a m a n n e r s i m i l a r to that of i n t e r g r a n u l a r s t r e s s - c o r r o sion c r a c k i n g in b a s e m e t a l s , one would e x p e c t to obs e r v e " i n t e r p h a s e - i n t e r f a c e " to t r a n s g r a n u l a r s t r e s s c o r r o s i o
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