The effect of morphology on the strength of pearlite
- PDF / 762,067 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 206 Views
AND
B. L. BRAMFITT
The effects of v a r i o u s m o r p h o l o g i c a l f e a t u r e s on the strength of h i g h - p u r i t y p e a r l i t e w e r e studied. A continuous-cooling mode of t r a n s f o r m a t i o n f r o m different a u s t e n i t i z i n g t e m p e r a t u r e s was used to produce v a r i a t i o n s in a v e r a g e nodule d i a m e t e r and minimum i n t e r l a m e l l a r spacing. It was found that, for a constant t r a n s f o r m a t i o n t e m p e r a t u r e , nodule s i z e was d i r e c t l y r e l a t e d to p r i o r anstenite grain size. On the other hand, minimum i n t e r l a m e l l a r spacing is c o n t r o l l e d by t r a n s f o r m a t i o n t e m p e r a t u r e , independent of p r i o r austenite grain s i z e and nodule s i z e . Both the yield strength and f r a c t u r e s t r e s s of p e a r l i t e was found to be i n v e r s e l y p r o p o r t i o n a l to i n t e r l a m e l l a r spacing and independent of p r i o r a u stenite grain s i z e and nodule size.
MAJOR
p e a r l i t e investigations l-s have e s t a b l i s h e d that growth d a r i n g the i s o t h e r m a l t r a n s f o r m a t i o n of austenite to p e a r l i t e is always nodular and that t h e s e p e a r l i t e nodules develop and grow f r o m a number of nuclei located in the p r i o r austenite grain boundary until they impinge upon one another, l'e Within each nodule t h e r e a r e colonies ~ of a l t e r n a t i n g f e r r i t e and cementite l a m e l l a e , each having a single orientation. The i n t e r l a m e l l a r spacing is dependent only on the t e m p e r a t u r e of t r a n s f o r m a t i o n . 4 The p r i o r austenite g r a i n s i z e affects p e a r l i t e nodule s i z e but a p p a r e n t l y has no effect on i n t e r l a m e l t a r spacing. ~ Strength and h a r d n e s s of i s o t h e r m a l l y t r a n s f o r m e d eutectoid s t e e l s v a r y l i n e a r l y with t r a n s f o r m a t i o n t e m p e r a t u r e and with the l o g a r i t h m of the i n t e r l a m e l l a r spacing. 6'7 It was l a t e r found that a finer i n t e r l a m e l l a r spacing i n c r e a s e s the Charpy i m p a c t t r a n s i t i o n s t e m p e r a t u r e , s The effect of p r o c e s s i n g v a r i a b l e s , i.e., a u s t e n i t i z i n g t e m p e r a t u r e (austenite grain size) and i s o t h e r m a l bath t e m p e r a t u r e ( t r a n s f o r m a t i o n t e m p e r a t a r e ) on the s t r u c t u r a l f e a t u r e s , i.e., i n t e r l a m e l l a r spacing and nodule s i z e , b e c o m e s c r i t i c a l in the c a s e of the patenting p r o c e s s for s t e e l wire and rod. A c o n s i d e r a b l e amount of r e s e a r c h has been done on the v a r i a b l e s involved in the patenting p r o c e s s , g - n which is complicated by the fact that i n c r e a s e d thickness p r e v e n t s i s o t h e r m a l t r a n s f o r m a t i o n - - t h e outer p a r t o[ the rod is i s o t h e r m a l l y t r a n s f o r m e d w h e r e a s
Data Loading...
