Electrical resistivity and microstructural changes accompanying the isothermal decomposition of austenite in eutectoid s
- PDF / 478,818 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 67 Downloads / 201 Views
T H E o b j e c t of t h i s s t u d y was to d e r i v e an i s o t h e r m a l t r a n s f o r m a t i o n d i a g r a m b y an e l e c t r i c a l r e s i s t i v i t y m e t h o d and to c o m p a r e t h i s d i a g r a m with one d e r i v e d b y o p t i c a l m e t a l l o g r a p h y . The s t e e l u s e d c o n t a i n e d 0.77 p c t c a r b o n and 0.11 p c t m a n g a n e s e and was c h o s e n b e c a u s e a e u t e c t o i d c o m p o s i t i o n o f f e r s no c o m p l i c a t i o n s which would o c c u r due to p r o e u t e c t o i d r e a c t i o n s . T h e r e h a s b e e n only a v e r y l i m i t e d a m o u n t of w o r k done with r e g a r d to the s t u d y of i s o t h e r m a l p h a s e t r a n s f o r m a t i o n s in s t e e l s b y r e s i s t i v i t y c h a n g e s . Smith I in 1935 was the f i r s t to u s e r e s i s t i v i t y m e t h o d s to d e t e r m i n e i s o t h e r m a l 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 . He s t u d i e d e l e c t r i c a l c o n d u c t i v i t y and o t h e r p r o p e r t y c h a n g e s a s s o c i a t e d with an 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 a high m a n g a n e s e , h y p e r e u t e c t o i d s t e e l at 842~ and c o n c l u d e d that c o n d u c t i v i t y m e a s u r e m e n t s gave the f i r s t i n d i c a t i o n of s o m e change t a k i n g p l a c e in the s u p e r s a t u r a t e d s o l i d solution. Rote, e t a l . 2 w e r e the f i r s t to d e t e r m i n e an e n t i r e i s o t h e r m a l t r a n s f o r m a t i o n d i a g r a m b y t h i s m e t h o d . They d e r i v e d a c u r v e f o r a g r a y c a s t i r o n but v e r i f i e d t h e i r r e s u l t s b y o p t i c a l m e t a l l o g r a p h y at only two t e m p e r a t u r e s . C o l n e r and Z m e s k a l 3 d e s c r i b e d a s o m e w h a t m o r e s o p h i s t i c a t e d a p p a r a t u s for the s t u d y of the 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 of s t e e l by electrical resistivity changes. Their experiments, h o w e v e r , w e r e p r i m a r i l y d i r e c t e d t o w a r d the s t u d y of s t a i n l e s s s t e e l on continuous cooling. R a d c l i f f e and R o l l a s o n 4 e m p l o y e d r e s i s t i v i t y m e a s u r e m e n t s in t h e i r s t u d y of i s o t h e r m a l t r a n s f o r m a t i o n s in low a l l o y s t e e l s and i r o n - c a r b o n a l l o y s of e u t e c t o i d c o m p o s i t i o n in the b a i n i t e r a n g e . T h e i r o p t i c a l v e r i f i cation was l i m i t e d only to m e t a l l o g r a p h i c s t u d i e s of the s p e c i m e n s on c o m p l e t i o n of the r e s i s t i v i t y c h a n g e s . In a l l c a s e s t h e y found the s p e c i m e n s to be 100 p c t t r a n s f o r m e d a f t e r a l l r e s i s t i v i t y c h a n g e s had c e a s e d . Owen and White ~ a l s o s t u d i e d i s o t h e r m a l t r a n s f o r m a tions of low a l l o y s t e e l s in the b a i n i t e r a n g e but r e p o r
Data Loading...
