The rate of solution of nitrogen in liquid Fe-Se and Fe-Te alloys

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G. MOWERS

AND

ROBERT

D. PEHLKE

The k i n e t i c s of n i t r o g e n solution in liquid i r o n containing s m a l l a m o u n t s of s e l e n i u m and t e l l u r i u m have b e e n studied. The p r e s e n c e of t h e s e s u r f a c e a c t i v e e l e m e n t s m a r k e d l y d e c r e a s e s the r a t e of n i t r o g e n a b s o r p t i o n . The r e s u l t s a r e c o m p a r e d with p r e v i o u s s t u d i e s on F e - O and F e - S a l l o y s . The solution p r o c e s s is m o d e l e d in t e r m s of the c o n c e n t r a t i o n of the s u r f a c e a c tive e l e m e n t .

DISSOLVEDn i t r o g e n

has long b e e n r e c o g n i z e d a s having a m a r k e d e f f e c t on the p h y s i c a l p r o p e r t i e s of i r o n and i r o n al l o y s . Depending on s u b s e q u e n t t r e a t m e n t and d e s i r e d p r o d u c t u s a g e , t h e s e e f f e c t s m ay or m ay not be d e s i r a b l e . In s o m e i n s t a n c e s , d i s s o l v e d n i t r o g e n is c o n s i d e r e d h a r m f u l a s it i m p a i r s r o l l a bi l i t y ; in other c a s e s n i t r o g e n is d e l i b e r a t e l y added to i m p r o v e h a r d n e s s and a u s t e n i t e s t a b i l i t y . T h e r e f o r e , it would be of c o n s i d e r a b l e p r a c t i c a l s i g n i f i c an ce if e i t h e r the e q u i l i b r i u m solubility or r a t e of solution of n i t r o g e n in i r o n and i r o n a l l o y s could be controlled. B e c a u s e much of the n i t r o g e n p r e s e n t in the final pro d u ct is a r e s u l t of p r o c e s s i n g the i r o n in the liquid s t a t e , a g r e a t deal of r e s e a r c h has b e e n c a r r i e d out in r e c e n t y e a r s to d e t e r m i n e both the e q u i l i b r i u m s o l u b i l i t y and solution rate of n i t r o g e n in liquid i r o n and m a n y i r o n a l l o y s . ~-s In g e n e r a l , it h a s b e e n found that m o s t alloying e l e m e n t s , when p r e s e n t in c o n c e n t r a t i o n s of l e s s than 1 wt pct, have l i t t l e or no e f f e c t on e i t h e r e q u i l i b r i u m solubility or r a t e of solution. Notable e x c e p t i o n s which have b e e n d i s c u s s e d p r e v i o u s l y in the l i t e r a t u r e a r e the two s u r f a c e a c t i v e e l e m e n t s , oxygen and sulfur. 3-s T h i s study is a continuation of the ki n et i c work on s u r f a c e a c t i v e e l e m e n t s and i n c l u d e s two o t h e r Group VI e l e m e n t s , s e l e n i u m and t e l l u r i u m . The effect of the four Group VI e l e m e n t s on n i t r o gen solubility when p r e s e n t in c o n c e n t r a t i o n s of l e s s than 0.3 wt pct i s shown in Fig. 1. As can be s e e n by the expanded solubility s c a l e , th e s e e l e m e n t s have only a m i n o r e f f e c t on e q u i l i b r i u m solubility. The c u r v e s shown in Fig. 1 w e r e taken f r o m two s o u r c e s , which explains the two s l i g h t l y d i f f e r e n t s o l u b i l i t y v a l u e s for pure i r o n . T