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ments a r e dynamic in nature and t h e r e f o r e , a r e not limited to r e a s o n a b l e i s o t h e r m a l t e m p e r a t u r e s and t i m e s . It is this rapid d e t e r m i n a t i o n of a c c u r a t e kinetic p a r a m e t e r s that f a c i l i t a t e s p r o c e s s evaluation and design. These investigations were made using a DuPont 990 t h e r m a l a n a l y z e r and DSC cell. To simplify r e f e r e n c e selection; - 0 t e m p e r r e f e r e n c e s of the s a m e size and weight as the evaluated s a m p l e s were used. Heating r a t e s of 5, 10, 20, 35, 50, 75 and 100~ were used to evaluate heating r a t e effects and d e t e r m i n a t i o n of kinetic p a r a m e t e r s . F i g u r e 2 is a r e p r e s e n t a t i v e t h e r m o g r a m for a comm e r c i a l 1XXX s e r i e s alloy heated at 20~ The p r e s e n c e of multiple peaks in region " B " has been a t t r i b u t e d to vacancy motion and annihilation ( r e covery). Knoop hardness t e s t ( r o l l i n g direction; long t r a n s v e r s e ; short t r a n s v e r s e ) on s a m p l e s quenched from the indicated t e m p e r a t u r e s d e m o n s t r a t e large p r o p e r t y v a r i a t i o n s in common d i r e c t i o n s as well as t e x t u r a l d i f f e r e n c e s . DSC peaks, however, have shown to be r e p r o d u c i b l e to +0.5~ and a r e not a function of testing d i r e c t i o n . M e t a l l o g r a p h i c evaluation of these s a m p l e s show no m i c r o s t r u c t u r a l changes, i.e. nucleation. The m a j o r peak, " A " , on this t h e r m o g r a m is well defined and is shown in F i g . 2 to be a s s o c i a t e d with the annealing r e a c t i o n of r e c r y s t a l l i z a t i o n . The DSC peak maximum, 398 ~C (748~ c o r r e s p o n d s d i r e c t l y with the o v e r a l l drop in h a r d n e s s v a l u e s . (Hardness values do show sheet t e x t u r a l d i f f e r e n c e s . ) The onset of peak " A " also defines the initiation of the r e c r y s t a l lization r e a c t i o n as shown by both h a r d n e s s (see F i g . 21 and m e t a l l o g r a p h i c evaluations (see F i g . 3). R e c r y s t a l l i z a t i o n is a t h e r m a l l y a c t i v a t e d p r o c e s s during which s t r a i n free g r a i n s nucleate and grow from PROSESSIN6

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STRUCTURE

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Fig. 1-Schematic representation of the influences of structure, properties arid processing upon each other.

ISSN 0360-213317910013-1045500.7510 1979 AMERICAN SOCIETY FOR METALS AND THE M E T A L L U R G I C A L SOCIETY OF AIME

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