Nitrogen solubility in liquid Fe-Ta, Fe-Cr-Ta, Fe-Ni-Ta, and Fe-Cr-Ni-Ta alloys
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WADA
AND
ROBERT
D. PEHLKE
The n i t r o g e n s o l u b i l i t y in liquid F e - T a , F e - C r - T a , F e - N i - T a , and F e - 1 8 pct C r - 8 pct N i - T a a l l o y s was m e a s u r e d using the S i e v e r t s ' method 9 The e x p e r i m e n t s c o v e r e d the t e m p e r a t u r e r a n g e f r o m 1782 to 2031 K, and t a n t a l u m contents f r o m 2.0 to 20.0 wt pct T a . N i t r o g e n solution o b e y e d S i e v e r t s ' law and no n i t r i d e p r e c i p i t a t i o n was o b s e r v e d in this c o n c e n t r a t i o n r a n g e . T a n t a l u m i n c r e a s e s the n i t r o g e n s o l u b i l i t y and the heat of solution of n i t r o g e n is m o r e n e g a t i v e at h i g h e r t a n t a l u m contents in t h e s e a l l o y s . The e x c e s s enthalpy and e n t r o p y of solution of n i t r o g e n w e r e d e t e r m i n e d . The f i r s t and s e c o n d o r d e r i n t e r a c t i o n p a r a m e t e r s between n i t r o g e n and t a n t a l u m w e r e d e t e r m i n e d a s a function of t e m p e r a t u r e , e Ta = - 1 0 1 . 7 / T + 0.018 and e TaTa = - 3 . 2 7 / T + 0.0022. The effects of a l l o y ing e l e m e n t s on the a c t i v i t y c o e f f i c i e n t of n i t r o g e n w e r e m e a s u r e d and the s e c o n d o r d e r c r o s s - i n t e r a c t i o n p a r a m e t e r s b e t w e e n n i t r o g e n and T a with C r and Ni w e r e d e t e r m i n e d at 1873 K a s e~rTa : 0 9 and e NiTa = 0 9149
T H E b e h a v i o r of n i t r o g e n in m u l t i c o m p o n e n t F e - C r Ni b a s e a l l o y s , including the influence of v a r i o u s c o n c e n t r a t i o n s of a l l o y i n g e l e m e n t s and n i t r i d e p r e c i p i t a tion, has been r e c e n t l y m e a s u r e d by the p r e s e n t a u t h o r s 1-3 T a n t a l u m is often p r e s e n t in s t e e l s c o n taining nitrogen; however, a s s e s s m e n t s of its effect on n i t r o g e n b e h a v i o r , i.e. the i n t e r a c t i o n p a r a m e t e r s and t h e i r t e m p e r a t u r e d e p e n d e n c y , and t a n t a l u m n i t r i d e f o r m a t i o n , have been s o m e w h a t c o n t r a d i c t o r y 9 P e h l k e and E l l i o t t 4 d e t e r m i n e d the f i r s t o r d e r i n t e r a c t i o n p a r a m e t e r , e Ta, in dilute liquid F e - T a a l l o y s at 1873 K. E v a n s and P e h l k e 5 m e a s u r e d the e q u i l i b r i u m between n i t r o g e n and t a n t a l u m in liquid i r o n and d e t e r m i n e d the f i r s t o r d e r i n t e r a c t i o n p a r a m e t e r for the t e m p e r a t u r e r a n g e f r o m 1823 to 1973 K. T h e y a l s o o b s e r v e d t a n t a l u m n i t r i d e f o r m a t i o n at 1823 K in a 20.2 pct T a a l l o y . S m a l l and P e h l k e 6 m e a s u r e d the effect of t a n t a l u m on n i t r o g e n s o l u b i l i t y in liquid F e - 1 8 p c t C r - 8 pct Ni a l l o y s up to 11 pct T a at 1873 K. M o r i t a el al 7 m e a s u r e d the n i t r o g e n s o l u b i l i t y and n i t r i d
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