Stability and mechanical properties of some metastable austenitic steels
- PDF / 1,959,343 Bytes
- 13 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 225 Views
One of the i m p o r t a n t p r o c e s s i n g s t e p s is the prior deformation of the austenite ( h e r e a f t e r a b b r e v i a t e d a s PDA). The p r i m a r y p u r p o s e of such d e f o r m a t i o n i s to r a i s e the y i e l d s t r e n g t h of the a u s t e n i t e to 200,000 p s i or above. To a c h i e v e this o b j e c t i v e , a l a r g e amount of d e f o r m a t i o n (70 to 80 pet) at a t e m p e r a t u r e b e t w e e n 200 ~ and 450~ i s r e q u i r e d . M i c r o s t r u c t u r a l and c h e m i c a l changes which a l t e r a u s t e n i t e s t a b i l i t y and m e c h a n i c a l p r o p e r t i e s can o c c u r during t h i s t r e a t m e n t . The f i r s t o b j e c t i v e of this study was to identify t h e s e c h a n g e s by s y s t e m a t i c a l l y v a r y i n g the c h e m i c a l c o m p o s i t i o n , the p r o c e s s i n g p r o c e d u r e and the t e s t i n g c o n d i t i o n s . The s e c o n d o b j e c t i v e w a s to r e l a t e the v a r i a t i o n s in a u s t e n i t e s t a b i l i t y to the m e c h a n i c a l p r o p e r t y c h a n g e s . S t e e l s of w i d e l y d i f f e r i n g c o m p o s i t i o n s and p r o c e s s i n g h i s t o r i e s w e r e s t u d i e d , including a) a s e r i e s of c a r b o n l e s s F e - N i a l l o y s of v a r y i n g a u s t e n i t e s t a b i l i t y ; b) a s t e e l containing n i c k e l and c a r b o n without a s t r o n g c a r b i d e f o r m e r , and c) a s e r i e s of s t e e l s of v a r y i n g s t a b i l i t y containing n i c k e l , c a r b o n , c h r o m i u m , and m a n g a n e s e . The w e a k e r c a r b o n l e s s F e - N i a l l o y s w e r e s t u d i e d b e c a u s e the c h a n g e s induced by p r o c e s s i n g w e r e l i m i t e d to those of s t r u c t u r e . C h e m i c a l c h a n g e s w e r e a d d i t i o n a l l y induced by p r o c e s s i n g in the F e - N i - C and the F e - N i - C r - M n - C s t e e l s . In the l a t t e r , the effect of a m o d e r a t e l y s t r o n g c a r b i d e f o r m e r ( c h r o m i u m ) was s t u d i e d . E X P E R I M E N T A L PROCEDURE H e a t s of a p p r o x i m a t e l y 15 lbs w e r e m e l t e d in a h e l i u m a t m o s p h e r e , c a s t in heavy c o p p e r m o l d s and s u b s e q u e n t l y a n n e a l e d in a n e u t r a l a t m o s p h e r e for 3 d at ll00~ The ingots w e r e f o r g e d at l l 0 0 ~ into p l a t e s 289 by -~ in. in c r o s s s e c t i o n , which w e r e s u g s e q u e n t l y r e d u c e d by r o l l i n g a t 450~ to 1 a t h i c k n e s s of ~ in. The p l a t e s w e r e a u s t e n i t i z e d and b r i n e quenched. The c a r b o n l e s s a l l o y s w e r e held at 1150~ for -~ h and the c a r b o n containing s t e e l s , at 1200~ f o r 2 h. The final d e f o r m a t i o n (70 pct) was c a r r i e d out at PDA t e m p e r a t u r e s o f - 1 2 0 ~ 25 ~ 100 ~ 150 ~ 200 ~ 250 ~ 300% and 450~ ( e x c e p t w h e r e o t h e r V O L U M E 3, O C T O B E R 1 9 7 2 - 2
Data Loading...
