Thermomechanical treatment and transformation characteristics of Fe-Mn austenites
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THERMOMECHANICAL treatment entailing deformat i o n - i n d u c e d t r a n s f o r m a t i o n has b e e n shown to e n hance t e n s i l e s t r e n g t h and d u c t i l i t y of m e t a s t a b l e C r - N i a u s t e n i t e s . l In a n o t h e r p a p e r , 2 we have shown that m a n g a n e s e a u s t e n i t e s can be a p p r e c i a b l y s t r a i n - h a r d e n e d by an a u s f o r m i n g t r e a t m e n t . The s a m e a l l o y s were used h e r e , to study the s t r a i n - i n d u c e d t r a n s f o r m a t i o n c h a r a c t e r i s t i c s following a u s f o r m i n g t r e a t m e n t , and to evaluate the e x t e n t to which these m a n g a n e s e s t e e l s may p o s s e s s the p r o p e r t i e s of a c l a s s of a l l o y s c o m m o n l y r e f e r r e d to a s " T R I P " s t e e l s . EXPERIMENTAL Materials Some of the F e - M n a l l o y s used p r e v i o u s l y to study the s t r a i n - h a r d e n i n g c h a r a c t e r i s t i c s of m e t a s t a b l e a u s t e n i t e z were used in this work. T h e i r c h e m i c a l a n a l y s e s a r e given in T a b l e I. A s - r e c e i v e d m a t e r i a l s were m a c h i n e d to r e m o v e the d e c a r b u r i z e d l a y e r , and cut into -~ in. wide s t r i p s of different t h i c k n e s s .
Table I. Chemical Analysesand Solution Treating Temperatures
Alloy
Pet Mn
Pet C
Pet Alloying Element
BI B2 B4
15.1 13.8 13.8
041 0.42 0.39
3 Cr 2.9 Mo
~ SolutionTreating Temperature
1050 1050 1050, 1100
1 in. gage length (and all 0.05 in. thick) were ground and t e s t e d in a U n i v e r s a l I n s t r o n T e s t i n g Machine at a c r o s s h e a d s p e e d of 0.05 ipm. In a n o t h e r e x p e r i m e n t , a f t e r v a r y i n g a m o u n t s of a u s f o r m i n g , s a m p l e s were r o l l e d at r o o m t e m p e r a t u r e (to be r e f e r r e d to as c o l d - r o l l i n g in f u r t h e r d i s c u s sion), t e m p e r e d at 200~ for 1 hr and t e s t e d , a s b e f o r e . A few u n a u s f o r m e d s a m p l e s w e r e c o l d - r o l l e d to v a r y ing e x t e n t s , t e m p e r e d and t e s t e d . A g a i n , all t e n s i l e s a m p l e s w e r e 0.05 in. thick.
X-Ray Examination T h e r m o m e c h a n i c a l T r e a t m e n t and T e n s i l e T e s t i n g S a m p l e s were s o l u t i o n - t r e a t e d for 1 hr in a n a r g o n a t m o s p h e r e at 1050 ~ or l l 0 0 ~ a s shown in T a b l e I, and s u b s e q u e n t l y w a t e r - q u e n c h e d . An a u s t e n i t i c s t r u c t u r e was obtained in all a l l o y s , and a few u n d i s s o l v e d c a r bide p a r t i c l e s were n o t i c e d in the m o l y b d e n u m - b e a r i n g alloy solution t r e a t e d at 1050~ The a s - q u e n c h e d s a m p l e s were r e h e a t e d in a salt b a t h , m a i n t a i n e d at 500 ~ or 550~ for 10 m i n and then r o l l e d for v a r y i n g a m o u n t s of a u s t e n i t e d e f o r m a t i o n (to be r e f e r r e d to a s a u s f o r m i n g , in f u r t h e
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