Lattice dilation of 25cr-28ni and 25cr-28ni-2mo austenitic steels by dissolved nitrogen
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s t r a i n r a t i o , o r r m value, has been s a t i s f a c t o r i l y taken as a qualitative i n d i c a t o r f o r the t e x t u r e of the s p e c i men. An ~)n value of ~1 i n d i c a t e s that the t e x t u r e is n e a r l y random; when r m i s c o n s i d e r a b l y g r e a t e r than 1, the t e x t u r e will be s t r o n g l y (111) with v e r y l i t t l e (100); and when r is s u b s t a n t i a l l y t e s s than I, the t e x t u r e will be g r e a t l y weakened in (111), but s t r e n ~ h e n e d in (100). The e x t r a p o l a t e d re value does not have such useful f e a t u r e s . D r . T r u s z k o w s k i i m p l i e s that the v a r i a t i o n of the s t r a i n r a t i o with d e g r e e of s t r a i n i n g is a consequence of t e x t u r a l changes during t e n s i l e d e f o r m a t i o n . But j u s t how these effects occur has not been e l a b o r a t e d in any of his work. Understandably, the r e a l situation is v e r y complex, b e c a u s e a n i s o t r o p i c work hardening, in the a u t h o r ' s opinion, must be c o n s i d e r e d in o r d e r to explain the o b s e r v e d s t r a i n dependence of the r values. The t e x t u r a l changes d u r i n g t e n s i l e d e f o r m a t i o n of sheet s t e e l s have been studied by s e v e r a l workers.8'~ It was shown ~ that from a n e a r l y random textured s p e c i m e n the t e x t u r e changes during uniform elongation toward (111) [110], an orientation which should yield high r v a l u e s . ~~ Yet the r values were o b s e r v e d to r e m a i n p r a c t i c a l l y unchanged during uniform elongation. ~ This may indicate that e i t h e r the s t r a i n r a t i o is not sufficiently s e n s i t i v e to the t e x t u r a l changes since the (111) [110] t e x t u r e developed at the end of uniform elongation is s t i l l r e l a t i v e l y weak, o r the a n i s o t r o p i c work hardening as the t e x t u r e develops o v e r c o m p e n s a t e s the effect of o r i e n t a t i o n a l changes on the r v a l u e s . M o r e r e c e n t l y , Delayen and P a r n i e r e 9 showed that, b a s e d on s p a t i a l o r i e n t a t i o n d i s t r i b u t i o n a n a l y s i s , the volume of c r y s t a l l i t e s having (111) [110 ] orientation i n c r e a s e s by 90 pct in a textured l o w - c a r bon s t e e l s p e c i m e n a f t e r 20 pct elongation, which is in e s s e n t i a l a g r e e m e n t with the a u t h o r ' s r e s u l t s lz on the s p e c i m e n s t e s t e d . Even though the volume f r a c t i o n s of this p a r t i c u l a r orientation, a c c o r d i n g to Delayen and P a r n i e r e , 9 w e r e only about 4 pet at z e r o s t r a i n to 7.5 pct at 20 pet elongation, which a r e not v e r y g r e a t , the i n c r e a s e in this o r i e n t a t i o n during t e n s i l e d e f o r mation should not cause a d e c r e a s e in the r value. Yet the r value was found to d e c r e a s e consistently with inc r e a s i n g s t r a i n . ~,5 These o b s e r v a t i o n s indicate
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