Interphase precipitation of cementite in a continuously-cooled plain-carbon steel
- PDF / 1,361,802 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 68 Downloads / 196 Views
Fig. 6--Same a s Fig. 3 . Tin X - r a y i m a g e , magnification 540 times.
Table I . Microprobe Analysis
Unoxidized Core Case: Oxides* Matrix
Ag(t-a)
Composition, Wt Pct S, (t-a)
Cd (L-a)
90.5 3.0 98.0
0.12 6.80 0.002
8.00 78,50 0.004
*May include slight excitation of matrix.
o x i d a t i o n a f t e r 96 h r a t 8 0 0 ° C w a s 0.99 m m v s 1.14 m m for the s t a n d a r d m a t e r i a l . CONC LUSIONS 1) D u r i n g i n t e r n a l o x i d a t i o n o f A g - C d - S n a l l o y s , t h e o x i d e p a r t i c l e s g r o w a s a n i n t i m a t e m i x t u r e of t h e o x i d e s of c a d m i u m a n d t i n . 2) T h e l a r g e d i f f e r e n c e i n t h e d r i v i n g f o r c e f o r t h e formation of oxides between c a d m i u m and tin ( f r e e ene r g i e s o f f o r m a t i o n per oxygen a t o m , at 800°C are - 2 7 . 8 k c a l a n d --44.2 ken1 f o r CdO a n d S n O 2 , r e s p e c t i v e l y z) m a k e s r e a s o n a b l e t h e e x p e c t a t i o n that e a r l y f o r m a t i o n of t h e o x i d e w i t h l o w e r f r e e e n e r g y o f f o r m a t i o n ~ ( i . e , SnO2), a c t s as a nucleating a g e n t f o r t h e g r o w t h o f CdO p a r t i c l e s . T h e f o r m a t i o n of s p i k e s w h i c h i s d e p e n d e n t on t h e r e l a t i o n s h i p b e t w e e n g r a i n c r y s t a l orientation and the direction of motion of the oxidation front r e s u l t s from t h e influence of tin a n d / o r tin oxide o n t h e various p a r t i c l e g r o w t h p a r a m e t e r s , i . e . s u r f a c e e n e r g i e s , oxygen and c a d m i u m distributions, diffusion r a t e s of different elements, and s u p e r saturation levels. W o r k on t h e s e s y s t e m s i s c o n t i n u i n g . W e w o u l d l i k e t o a c k n o w l e d g e M r . G. B r u n o o f A d v a n c e d M a t e r i a l s R e s e a r c h in B u r l i n g t o n , M a s s . w h o made t h e e l e c t r o n p r o b e measurements.
1. J. H. Brophy, R. M, Ro~e, andJ. Wulff: The Structure and Properties o.f Materials, John Wiley & Sons, Inc., 1964. 2. C. E. Wicks and F. E. Block: Thermodynamic Properties o f 65 Elements, Bull. 605, Bur. Mines, 1963.
2962-VOLUME 2 , OCTOBER 1971
AND P . C, B E C K E R
A S a r e s u l t o f s e v e r a l i n d e p e n d e n t i n v e s t i g a t i o n s into t h e d e c o m p o s i t i o n o f a u s t e n i t e in a l l o y s t e e l s , l - 4 a n e w e u t e c t o i d t r a n s f o r m a t i o n h a s b e e n r e c o g n i z e d in w h i c h f e r r i t e g r o w s in c o n j u n c t i o n w i t h t h e r e p e a t e d n u c l e a tion of a l l o y c a r b i d e s on the moving austenite-ferrite interphase boundary. T h e reaction has been t e r m e d " i n t e r p h a s e " precipitation a s b o t h t h e distribution as well a s t h e c r y s t a l l o g r a p h y o f t h e c a r b i d e s a r e influe n c e d by t h e i n t e r p h a s e b o u n d a r y . 3'~ T h e c a r b i d e s a r e not r a n d o m l y d i s p e r s e d but a r e a r r a n g e d i n s h e e
Data Loading...
