Effect of thermomechanical processing on fatigue crack propagation
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S I G N I F I C A N T changes in m e c h a n i c a l p r o p e r t i e s and m e t a l l u r g i c a l s t r u c t u r e can occur as a r e s u l t of m e c h a nical a n d / o r t h e r m a l t r e a t m e n t making it i m p o r t a n t to understand the r o l e of v a r i o u s m e t a l l u r g i c a l p r o c e s s e s on fatigue and f r a c t u r e of m e t a l s . F u r t h e r m o r e , such p r o c e s s e s can give r i s e to a n i s o t r o p i c behavior of the m a t e r i a l . D i r e c t i o n a l i t y of p r o p e r t i e s can a r i s e f r o m two s o u r c e s : a) c r y s t a l l o g r a p h i c texturing produced by r e o r i e n t a t i o n of g r a i n s in a p r e f e r r e d d i r e c t i o n during d e f o r m a t i o n or after annealing, and b) mechanical fib e r i n g r e s u l t i n g from alignment of inclusions and s e c ond phase constituents in the p r i n c i p a l d i r e c t i o n of working. S e v e r a l studies of d i r e c t i o n a l i t y as r e l a t e d to fatigue c r a c k propagation (FCP) have been conducted. Schijve 1'2 and o t h e r s s r e p o r t e d that c r a c k propagation r a t e s for s p e c i m e n s of 2024-T3 aluminum loaded t r a n s v e r s e to the rolling d i r e c t i o n were m o r e rapid than those of s p e c i m e n s loaded p a r a l l e l to the rolling d i r e c tion. More r e c e n t l y , H e i s e r and H e r t z b e r g o b s e r v e d s t r o n g a n i s o t r o p y with r e g a r d to F C P in banded hot r o l l e d steel; they o b s e r v e d i n c r e a s i n g r e s i s t a n c e to F C P in a r r e s t e r , divider, and short t r a n s v e r s e o r i e n tation, r e s p e c t i v e l y .4 A s y s t e m a t i c investigation is n e c e s s a r y to develop a c l e a r e r understanding of F C P as affected by m a t e r i a l p r o c e s s i n g . In p a r t i c u l a r , it is d e s i r a b l e to define the r e l a t i v e i m p o r t a n c e of c r y s t a l l o g r a p h i c and f i b e r text u r e s upon fatigue c r a c k propagation. T h e r e f o r e , the objectives of this study were to investigate the effect of m e c h a n i c a l p r o c e s s i n g and heat t r e a t m e n t on the extent of m a c r o s c o p i c and m i c r o s c o p i c F C P a n i s o t r o p y .
J. H. WEBER is Research Metallurgist, The International Nickel Company, Inc., Paul D. Merica Research Laboratory, Suffern, N. Y. 10901. R. W. HERTZBERG is Associate Professor, Department of Metallurgy and Materials Science, Lehigh University, Bethlehem, Pa. 18015. Manuscript submitted August 16, 1971. METALLURGICAL TRANSACTIONS
EXPERIMENTAL PROCEDURES M a t e r i a l s and P r o c e s s i n g T r e a t m e n t s C a r t r i d g e b r a s s (70 c o p p e r - 3 0 zinc) and type 305 s t a i n l e s s s t e e l w e r e used in this investigation, Table I. These m a t e r i a l s were chosen because of their strong tendency for p l a n a r slip wherein c r y s t a l l o g r a p h i c effects on fatigue c r a c k growth could be m a x i m i z e d . This was of
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