Martensite plate arrangements in 01 tool steel
- PDF / 1,222,174 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 99 Downloads / 211 Views
CHENANDP.
G. WINCHELL
In a c o m m e r c i a l 01 tool s t e e l a u s t e n i t i z e d at 1200~ m a r t e n s i t e plates form in s m a l l c l u s t e r s within a u s t e n i t e which has b e e n p a r t i t i o n e d by g r a i n b o u n d a r i e s and p r e e x i s t i n g m a r t e n s i t e p l a t e s . But the s u r f a c e of m a r t e n s i t e plate m i d - p l a n e s i n c r e a s e s only about one fourth as r a p i d l y and the plates a r e about six t i m e s as long as would be expected f r o m r a n d o m f o r m a t i o n in a u s t e n i t e r a n d o m l y p a r t i t i o n e d by p r e e x i s t i n g p l a t e s . M a r t e n site plates m a i n t a i n a constant t h i c k n e s s u n t i l t h e i r r a d i u s is r e s t r i c t e d to a p p r o x i m a t e l y the d i s t a n c e which i s tip affected, about 10 p m . The plate t h i c k n e s s to r a d i u s r a t i o is not constant. T H E n u c l e a t i o n of m a r t e n s i t e and its r a p i d growth into fully developed p l a t e s has b e e n a s e r i o u s c o n c e r n for m a n y y e a r s . In e x p e r i m e n t a l studies the c o m p l e x p r o b l e m of d e t e r m i n i n g i n d e p e n d e n t n u c l e a t i o n e v e n t s f r o m e x a m i n a t i o n of p a r t i a l l y t r a n s f o r m e d m i c r o s t r u c t u r e s is s t i l l s i g n i f i c a n t . The study of the g e o m e t r i c a l a r r a n g e m e n t s of m a r t e n s i t e p l a t e s has d i r e c t a p p l i c a t i o n in s p e c i f y i n g the m i c r o s t r u c t u r e s of h a r d e n e d s t e e l s . C o m p a r e d to i t s t h e o r e t i c a l and p r a c t i c a l i n t e r e s t , this study has r e c e i v e d l e s s a t t e n t i o n than is appropriate. The b a s i c idea of t h e o r e t i c a l t r e a t m e n t s of m a r t e n s i t e morphology is that the p l a t e s p a r t i t i o n the a u s t e n i t e c r y s t a l s into s m a l l e r r e g i o n s in which new p l a t e s form and f u r t h e r p a r t i t i o n the r e m a i n i n g u n t r a n s f o r m e d m a t r i x . F i s h e r 1 made an a d h o c a s s u m p tion that each plate t r a n s f o r m s a constant f r a c t i o n of the u n t r a n s f o r m e d c o m p a r t m e n t in which it f o r m s and that the n - t h plate f o r m s i n a c o m p a r t m e n t which is one n - t h the v o l u m e of that of the f i r s t plate. T h i s a p p r o a c h and m o d i f i c a t i o n s of it have b e e n widely used but definitive e x p e r i m e n t a l v e r i f i c a t i o n has not b e e n f o r t h c o m i n g . In fact M c M u r t r i e and Magee 2 s t u d y i n g two v e r y high n i c k e l alloys, in which b u r s t s of m a r t e n s i t e d o m i n a t e d the t r a n s f o r m a t i o n , concluded that the volume p e r m a r t e n s i t e plate was i n d e p e n d e n t (amazingly) of the n u m b e r of p l a t e s a l r e a d y f o r m e d . One would i n t u i t i v e l y guess that this conc l u s i o n is r e s t r i c t e d to
Data Loading...
