Influence of dislocation substructure on recrystallization in type 304 stainless steel
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(b) Fig. /--Typical dislocation substructures of 304 stainless steel tensile deformed to rupture at 500°C. Indices (hkl) give tensile axis and approximate beam orientation, Double exposure without correction for relative rotation between image and diffraction pattern in (b). VOLUME 8A, JANUARY 1977-213
above, s S a m p l e for electron microscopy were prep a r e d by c o n v e n t i o f i a l t e c h n i q u e s f r o m t r a n s v e r s e s l i c e s c u t by s p a r k e r o s i o n . T y p i c a l e x a m p l e s of t h e c e l l u l a r a n d p l a n a r disl o c a t i o n d i s t r i b u t i o n in t h e d e f o r m e d m a t e r i a l a r e
(a)
(b) F i g . 2--Effect of annealing for 10 min a t 900°C. Indices (hkl> g i v e t e n s i l e a x i s and approximate beam orientation. 214-VOLUME 8A, JANUARY 1977
s h o w n i n F i g . l ( a ) a n d (b), r e s p e c t i v e l y . D i s l o c a t i o n d e n s i t i e s i n t h i s c o n d i t i o n a r e o b v i o u s l y too h i g h t o be c o u n t e d q u a n t i t a t i v e l y . T h e r e f o r e , a d i f f e r e n c e in d i s l o c a t i o n d e n s i t y b e t w e e n t h e two s u b s t r u c t u r e s c a n n o t be r u l e d o u t a n d m a y a f f e c t t h e d r i v i n g
(a)
(b) Fig. 3--Effect of annealing for 15 rain at 900°C. i n d i c e s (hkl} give t e n s i l e axis a n d approximate b e a m o r i e n t a t i o n . METALLURGICAL TRANSACTIONS A
f o r c e for subsequent recrystallization. In fact, the cellular substructure, believed t o form u n d e r conditions which facilitate c r o s s slip, may well be a s s o c i ated with a l a r g e r mean free path for dislocation g l i d e and a l a r g e r rate of dislocation annihilation,
(aJ
(b)
Fig. 4--Effect of annealing for 20 min at 900°C. Indices ( h k l ) give tensile axis and approximate beam orientation. METALLURGICAL TRANSACTIONS A
leading t o lower dislocation densities at a given tensile strain. Such a difference in dislocation density, howe v e r , would merely be a consequence of the formation of different dislocation structures. It is therefore believed that u s i n g the same alloy for different substructures, any differences observed in annealing behavior may be attributed directly t o different dislocation arrangements. F i g s . 2 through 4 show the annealing sequence of cellular and p l a n a r deformation substructure, r e p r e sented by g r a i n s with tensile axes of 4100) and 4110), respectively. All photographs were taken with foils c l o s e t o the horizontal position in the microscope. Beam directions are therefore always nearly p a r a l l e l t o the directions of applied stress. No recrystallization was observed in any g r a i n a f t e r 5 min at 900°C. At 10 min and thereafter, planar deformation substructures were no longer found, and (110} orientations were only observed in recrystallized grains, F i g s . 2(b), 3(b) and 4(b). On the other hand, a merely r e c o v e r e d cellular deformation substructure in 4100) orientations persisted a f t e r 10 and 15 m
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