A correlation between the hot-hardness and the hot-tensile properties of AISI 304 stainless steel
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JOHN M O T E F F AND P A U L R. SIEBER R e c e n t l y Cahoon z p r e s e n t e d an i m p r o v e d equation r e l a t i n g h a r d n e s s to u l t i m a t e s t r e n g t h of m e t a l s and a l l o y s . This equation is given a s :
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w h e r e a u Is the u l t i m a t e n o m i n a l s t r e s s , H is the V i c k e r s P y r a m i d H a r d n e s s and n the s t r a i n h a r d e n i n g c o e f f i c i e n t a s r e l a t e d to the f a m i l i a r equation,
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Fig. 5 - - T h e effect of c a l c i u m c o n t e n t on the c a s e t h i c k n e s s of Ag-12.5 Cd alloy.
high e n e r g y I n t e r f a c e r e g i o n s . It is w e l l e s t a b l i s h e d 6 that the diffusion r a t e along g r a i n b o u n d a r i e s and high e n e r g y I n t e r f a c e s is h i g h e r than that within the g r a i n , hence an i n c r e a s e tn the c o n c e n t r a t i o n of such i n t e r f a c e s would i n c r e a s e the oxygen d i f f u s i o n r a t e t h r o u g h the a l l o y . 2. Effect on N u c l e a t i o n Rate for P r e c i p i t a t i o n . C a l c l u m f o r m s a much s t a b l e r oxide than c a d m i u m (at 800~ the f r e e e n e r g y of f o r m a t i o n of c a l c i u m oxide is - 124.7 k c a l , and that of c a d m i u m oxide is - 27.8 k c a l ) . T h e r e f o r e , the u n i f o r m l y d i s t r i b u t e d e l e m e n t a l c a l c i u m p a r t i c l e s o r a t o m s would be o x i d i z e d at a l o w e r oxygen c o n c e n t r a t i o n than would c a d m i u m . When oxygen d i f f u s e s into the s i l v e r a l l o y , the oxygen has a c o n c e n t r a t i o n p r o f i l e (vs d i s t a n c e f r o m the s u r f a c e ) such that the oxidation of Cadmium m a y not o c c u r r e a d ily in an unalloyed s i l v e r - c a d m i u m , but o x i d a t i o n of c a l c i u m wlth a s i m i l a r oxidation p r o f i l e i s v e r y l i k e l y . Once the CaO p a r t i c l e s do f o r m , h o w e v e r , t h e y can b e c o m e nuclei f o r the p r e c i p i t a t i o n of c a d m i u m oxide and enhance the r a t e of p r e c i p i t a t i o n of c a d m i u m oxide. P r e v i o u s i n v e s t i g a t i o n s of the oxidation of A g - 9 wt p c t c a d m i u m a l l o y with tin a s an a d d i t i v e have shown that all the tin a d d i t i v e b e c o m e s a s s o c i a t e d with the c a d mium-oxide particles. ? The a u t h o r s extend thanks to Dr. C. C. Liang of P. R. M a l l o r y and Co., Inc. for his v a l u a b l e s u g g e s t i o n s .
1. yon Cart Wagner: Z. Electrochera, 1959, vol. 63, no. 7, pp. 772-90. 2. Ernest Jest and E. Freudiger: The Kinetics and Thermodynamic of the lntenml Oxidation of Silver-Cadmium Alloys and the Arc Erosion Properties of the Oxidized Material, Proceeding Symposium on Electric Contact Phenomena, Univ. of Mass. 1961, pp. 177-97. 3. K. R. Comey, Jr. and T. J. Santala: U.S. Patent 3,472,654, Oct. 1969. 4. Y. S. Shen,
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