Mechanical properties of rare earth metal treated rail steels
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.01 P, 0.74 Mn and F e b a l a n c e (in weight p e r c e n t ) , and a n o t h e r f r o m the R E M - t r e a t e d r a i l s of the c o m p o s i t i o n 0.72 C, 0.12 Si, 0.02 S, 0.01 P , 0.72 Mn, 0.06 Ce, 0.04 La, and F e b a l a n c e . The t e s t s p e c i m e n s w e r e p r e p a r e d f r o m the head, web and b a s e of the r a i l s l a b s cut along both the l o n g i t u d i n a l and t r a n s v e r s e d i r e c t i o n s of r o l l i n g . The m i c r o s t r u c t u r e of both the c o n v e n t i o n a l and the R E M - t r e a t e d r a i l s t e e l s was hypoeutectoid; a m i x t u r e of p e a r l i t e c o l o n i e s and f e r r i t e g r a i n s with the a d d i t i o n a l f e r r t t e p r e c i p i t a t i o n along the p r i o r a u s t e n i t e grain boundaries. 8 The prior anstenite grains were c o a r s e and n o n u n i f o r m in s i z e (50 ~ 500 ~tm). The a v e r a g e p e a r l i t e colony s i z e was about 10 tzm with the a v e r a g e s p a c i n g of l a m e l l a e being 1 ~tm. T h e m a j o r change in the m i c r o s t r u c t u r e o b s e r v e d in the REM r a i l was the c o n v e r s i o n of MnS type i n c l u s i o n s into REM i n c l u s i o n s . F i g . 1 shows s o m e t y p i c a l MnS i n c l u s i o n s o b s e r v e d on the f r a c t u r e s u r f a c e s of the c a r b o n r a i l s t e e l , w h e r e a s F i g . 2 shows the REM i n c l u s i o n s in the R E M - t r e a t e d s t e e l . M o s t of the MnS i n c l u s i o n s have d e f o r m e d h e a v i l y along the r o l l i n g d i r e c t i o n and a p p e a r a s long r o d s o r e l l i p s o i d s . The REM i n c l u s i o n s , which a r e u s u a l l y h a r d e r than the s t e e l m a t r i x , r e m a i n r a t h e r u n d e f o r m e d and a r e s e e n a s s m a l l globular or angular particles. The chemical comp o s i t i o n of the i n d i v i d u a l i n c l u s i o n s was a n a l y z e d
Fig. 1 - R o d - or plate-like MnS inclusions on the impact fracture surfaces of the carbon rail steels (broken at 20~ METALLURGICAL TRANSACTIONS A
e i t h e r by an e l e c t r o n m i c r o p r o b e a n a l y z e r o r by an e n e r g y - d i s p e r s i v e X - r a y a n a l y z e r a t t a c h e d to the SEM. W h i l e m o s t of the s m a l l REM i n c l u s i o n s w e r e found to be e i t h e r RE s u l f i d e s o r RE o x y s u l f i d e s , 9 in a few c a s e s the REM i n c l u s i o n s w e r e a s s o c i a t e d with s o m e o x i d e s of A1203-FeO type, s u g g e s t i n g the l a t t e r t o be the p r e f e r e n t i a l n u c l e a t i o n s i t e s of the REM inclusions. M e c h a n i c a l p r o p e r t i e s of the r a i l s t e e l s w e r e o b t a i n e d b y the t e n s i l e , h a r d n e s s and i m p a c t t e s t s . T a b l e I s u m m a r i z e s the r e s u l t s of the s t a n d a r d t e n s i l e t e s t s p e r f o r m e d with both the c a r b o n r a i l and the REM r a i l s t e e l s . The a v e r a g e s t r e n g t h (0.2 pct YS) and u l t i m a t e t
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