Breakdown of primary grain boundary inhibition in 3 pct si-fe sheet
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Two a n n e a l s w e r e done at i n c r e m e n t s of 25~ o v e r the t e m p e r a t u r e r a n g e f r o m 1000 ~ to l l S 0 ~ All ann e a l s w e r e conducted in an Inconel tube f u r n a c e in a d r y h y d r o g e n a t m o s p h e r e (dew point ~ - 6 0 ~ Specim e n s w e r e in the f o r m of 1 in. c i r c u l a r d i s k s mounted u p r i g h t in a s m a l l s t a i n l e s s s t e e l b o a t . The annealing p r o c e d u r e was to c h a r g e the s p e c i m e n d i r e c t l y into the heating zone for a p r e d e t e r m i n e d t i m e , a f t e r which the c h a r g e was q u i c k l y d r a w n into a w a t e r - c o o l e d c h a m b e r . The lag t i m e to r e a c h t e m p e r a t u r e w a s d e t e r m i n e d by running a t r i a l a n n e a l at l l 0 0 ~ with a t h e r m o c o u p l e a t t a c h e d to the s p e c i m e n . The heating lag t i m e was a p p r o x i m a t e l y 15 s , c o r r e s p o n d i n g to a heating r a t e of about 70~ The cooling r a t e f r o m 1100 ~ to 400~ was s i m i l a r l y d e t e r m i n e d to be a p p r o x i m a t e l y 80~ The f i r s t s e r i e s of a n n e a l s was conducted for a p e r i o d of one h o u r , a s u f f i c i e n t t i m e for c o m p l e t i n g m o s t g r a i n growth processes. After annealing, these specimens w e r e m a c r o e t c h e d with Fe(NH4)(SO4)2 to r e v e a l the c o a r s e n e d g r a i n s t r u c t u r e . In a d d i t i o n , m a g n e t i c t o r q u e m e a s u r e m e n t s w e r e m a d e to c h a r a c t e r i z e the d e g r e e of (110)[001] t e x t u r e d e v e l o p m e n t . 4 The s e c o n d s e r i e s of a n n e a l s w a s conducted for a p e r i o d of 3 m i n . T h e s e s p e c i m e n s w e r e c h e m i c a l l y p o l i s h e d and then e t c h e d with 2 p c t HNO3-98 p c t C2HsOH. P r i m a r y g r a i n d i a m e t e r s w e r e d e t e r m i n e d by o p t i c a l m e t a l l o g r a p h y using a l i n e a r counting technique. 5 The e t c h e d s p e c i m e n s w e r e c o a t e d with c a r b o n in an a r c e v a p o r a t o r , s c o r e d , and r e e t c h e d to obtain c a r b o n e x t r a c t i o n r e p l i c a s . A S i e m e n s EM-100A E l e c t r o n M i c r o s c o p e was u s e d for the r e p l i c a a n a l y s e s . P a r t i c l e s i z e d e t e r m i n a t i o n s w e r e m a d e by m e a s u r i n g the d i a m e t e r s of p a r t i c l e s on e n l a r g e m e n t s of e l e c t r o n m i c r o graphs. RESULTS Selected macrographs of the specimens annealed for 1 h at temperatures between i000 ~ and I150~ are shown in Fig. i. Macrostructures of specimens annealed between I000 ~ and I075~ were comprised of predominately large secondary grains having diameters ranging from 3 to 5 mm and with minor amounts of coarsened primary grains having a grain size less than ~0.5 ram. Magnetic torque measurements, Fig. 2, confirmed that the secondary recrystallized matrix was of the (ii0)[001] orientation. Annealing at ll00~ and higher resulted in VOLUME 4, MARCH 1973
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