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g e n e r a l l y known that r e s i d u a l s t r e s s e s in case c a r b u r i z e d s t e e l s play a m a j o r r o l e in d e t e r m i n i n g the b a s i c (or unit) m e c h a n i c a l p r o p e r t i e s of the s t e e l s , and the o v e r a l l m e c h a n i c a l p e r f o r m a n c e of case c a r b u r i z e d components of s t r u c t u r e s . It is f u r t h e r known that this role may be e i t h e r b e e n f i c i a l or d e l e t e r i o u s . The n a t u r e of the role depends upon the sign and i n t e n s i t y of the peak s t r e s s e s , the complete d i s t r i b u t i o n of the s t r e s s e s in a l l t h r e e p r i n c i p a l d i r e c t i o n s , and the p a r t i c u l a r m e c h a n i c a l p e r formance characteristic under consideration. D e s p i t e the fact that the influence of r e s i d u a l s t r e s s e s on m e c h a n i c a l p r o p e r t i e s has b e e n o b s e r v e d e x p e r i m e n t a l l y in n u m e r o u s c a s e s , it is s t i l l difficult, if not i m p o s s i b l e , to r a t i o n a l i z e the effects o b s e r v e d , and even m o r e difficult to p r e d i c t in advance the q u a n t i t a t i v e effect that the r e s i d u a l s t r e s s e s will have in s p e c i f i c i n s t a n c e s . T h i s is the r e s u l t of s e v e r a l factors : 1) It is difficult to d e t e r m i n e q u a n t i t a t i v e l y the r e s i d u a l s t r e s s d i s t r i b u t i o n s in all t h r e e p r i n c i p a l d i r e c t i o n s without d e s t r u c t i v e t e s t i n g of the p a r t . The p r e s e n t status of n o n d e s t r u c t i v e m e a s u r e m e n t of r e s i d u a l s t r e s s e s l i m i t s the d e t e r m i n a t i o n to s u r f a c e s t r e s s e s only. 2) The a s - c a r b u r i z e d r e s i d u a l s t r e s s d i s t r i b u t i o n s m a y be a l t e r e d d u r i n g the p e r f o r m a n c e of the p r o p e r t y m e a s u r e m e n t t e s t beyond the extent which can be a n t i c i p a t e d f r o m the i m p o s e d s t r e s s state of the t e s t . T h e s e changes s t e m f r o m the in situ g e n e r a t i o n of a d d i t i o n a l i n t e r n a l s t r e s s e s as a r e s u l t of: a) the t e s t s t r a i n induced t r a n s f o r m a t i o n of a u s t e n i t e r e t a i n e d in the case of the c a r b u r i z e d p a r t , and b) the t e s t - s t r a i n induced i n t e r a c t i v e s t r e s s e s which r e s u l t f r o m the L, J. EBERTis Professor,Departmentof Metallurgyand MaterialsScience, CaseWesternReserveUniversity,Cleveland,OH44106. Thispaper is basedon a presentationmadeat a symposiumon "Carburizing and Nitridhag:Fundamentals,Processesand Properties"held at the Cincinnati Meetingof the MetallurgicalSocietyof AIME,November11 and 12, 1975under the sponsorshipof the Heat TreatmentCommittee. METALLURGICALTRANSACTIONSA

rheology of composite m a t e r i a l s , of which a case c a r b u r i z e d p a r t is an o u t s t a n d i n g e x a m p l e . T h i s p a p e r r e p r e s e n