The effects of phosphorus on the mechanical properties of low-carbon iron

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F e - P a l l o y s with n o m i n a l c o m p o s i t i o n s of 0.05, 0.1, 0.2, and 0.6 wt p c t P w e r e d e f o r m e d in c o m p r e s s i o n at t e m p e r a t u r e s b e t w e e n 77 and 295 K at s t r a i n r a t e s b e t w e e n 2.5 • 10 -4 and 3.5 • 10 -2 p e r s e e . The effect of g r a i n s i z e on the y i e l d s t r e n g t h w a s i n v e s t i g a t e d o v e r a r a n g e of about ASTM 7 to 3.5. The r e s u l t s show that the y i e l d s t r e n g t h of i r o n i s i n c r e a s e d 40 to 50 p e t in the 0.05 and 0.1 P a l l o y s at 295 K without affecting the notch i m p a c t t r a n s i t i o n t e m p e r a t u r e . At t e m p e r a t u r e s of 200 K and below s o l i d solution softening o c c u r s in a l l the a l l o y s e x c e p t f o r 0.6 p e t P. T h e d e g r e e of softening at a given t e m p e r a t u r e i s a function of the s t r a i n r a t e and g r a i n s i z e , being m o r e p r o n o u n c e d at h i g h e r s t r a i n r a t e s and larger grain sizes.

THIS i n v e s t i g a t i o n

i s c o n c e r n e d with the effect of p h o s p h o r u s on the l o w - t e m p e r a t u r e d e f o r m a t i o n of i r o n and i s p a r t of a l a r g e r p r o g r a m d e a l i n g with the i n f l u e n c e of a l l o y i n g e l e m e n t s on the m e c h a n i c a l p r o p e r t i e s of i r o n . P r e v i o u s i n v e s t i g a t i o n s h a v e been p r i m a r i l y c o n c e r n e d with the effect of p h o s p h o r u s on t h e t o u g h n e s s of i r o n and have shown that p h o s p h o r u s , l i k e o x y gen and n i t r o g e n , p r o d u c e s i n t e r g r a n u l a r w e a k n e s s in i r o n to an extent depending on the c o n c e n t r a t i o n of c a r bon and n i t r o g e n in the a l l o y . '-4 A d d i t i o n a l s t u d i e s h a v e c o n c e n t r a t e d on a n a l y s i s of p r e c i p i t a t i o n in F e - P a l l o y s f '6 On an a t o m b a s i s , the s t r e n g t h e n i n g p r o d u c e d by p h o s p h o r u s in i r o n i s g r e a t e r than that o b t a i n e d f r o m any o t h e r s u b s t i t u t i o n a l s o l u t e , v T h e r e f o r e , it a p p e a r e d d e s i r a b l e to i n v e s t i g a t e m o r e t h o r o u g h l y the m e c h a n i c a l p r o p e r t i e s of F e - P a l l o y s , and, in p a r t i c u l a r , the e f f e c t s of t e m p e r a t u r e , s t r a i n r a t e , g r a i n s i z e , and p h o s p h o r u s c o n c e n t r a t i o n on the l o w - t e m p e r ature mechanical properties. M A T E R I A L S AND PROCEDURES

F o u r t e e n kg ingots of n o m i n a l c o m p o s i t i o n s 0.05, 0.1, 0.2, and 0.6 wt p c t P w e r e m a d e by adding f e r r o p h o s p h o r u s to P l a s t i r o n (Type 104A). T h e f e r r o p h o s p h o r u s w a s p r e p u r i f i e d by m e l t i n g u n d e r an F e O s l a g . The P l a s t i r o n w a s m e l t e d and v a c u u m - c a r b o n - d e o x i d i z e d p r i o r to adding the p u r i f i e d f e r r o p h o s p h o r u

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