The effects of composition and carbide precipitation on temper embrittlement of 2.25 Cr-1 Mo steel: Part I. Effects of P
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RESEARCHinto the p r o b l e m
of t e m p e r e m b r i t t l e merit of a l l o y s t e e l s f r o m a p h e n o m e n o l o g i c a l point of view has o v e r a p e r i o d of many d e c a d e s involved e x p e r i m e n t s on both c o m m e r c i a l s t e e l s and s p e c i a l l y doped l a b o r a t o r y s t e e l s of c a r e f u l l y c o n t r o l l e d c o m p o s i t i o n . M o s t of o u r p r e s e n t u n d e r s t a n d i n g has c o m e f r o m the l a b o r a t o r y s t e e l s in which one f a c t o r at a t i m e could be v a r i e d . A s t h e s e s t u d i e s have p r o g r e s s e d the b e h a v i o r of the m o r e c o m p l i c a t e d c o m m e r c i a l s t e e l s has b e c o m e m o r e and m o r e u n d e r s t a n d a b l e . Up to the p r e s e n t t i m e m o s t of the l a b o r a t o r y s t u d i e s have e m p l o y e d s t e e l s containing Ni, u s u a l l y s i m p l e N i - C r s t e e l s , s i n c e t h e s e u s u a l l y exhibit the g r e a t e s t s u s c e p t i b i l i t y to t e m p e r e m b r i t t l e m e n t . H o w e v e r , o v e r the p a s t d e c a d e the r e a l i z a t i o n that C r - M o s t e e l s can a l s o be highly s u s c e p t i b l e has s p r e a d . T h e now f a m o u s H i n c k l e y Point t u r b i n e d i s c f a i l u r e in 1969 did much to s e t the s t a g e f o r the c u r r e n t i n t e r e s t in these steels. One of the m o s t w i d e l y used C r - M o s t e e l s for t h i c k w a l l e d s t r u c t u r a l a p p l i c a t i o n s has the b a s e c o m p o s i t i o n 2.25 C r - 1 Mo, and c o m m e r c i a l h e a t s g e n e r a l l y contain Mn and Si (added i n t e n t i o n a l l y ) a s w e l l a s r e s i d u a l l e v e l s of P and Sn which a r e p o t e n t i a l e m b r i t t l i n g e l e m e n t s . The p r e s e n t t w o - p a r t r e p o r t g i v e s the r e s u l t s of what i s a p p a r e n t l y the only c o m p r e h e n s i v e study for p u b l i c a t i o n of l a b o r a t o r y s t e e l s in which the 2.25 C r - 1 Mo c o m p o s i t i o n was u s e d a s a b a s e and the above e l e m e n t s w e r e a d d e d i n d i v i d u a l l y . The p r e s e n t p a p e r d e a l s with the e f f e c t s of P and Sn and P a r t II JIN YU is Post-doctoral Fellow, Max-Planck-Institut Fi~r Eisenforschung, 4 Di]sseldorf, West Germany. C. J. McMAHON, Jr. is Professor of Materials Science and Engineering, Department of Materials Science and Engineering, University of Pennsylvama, Philadelphia, PA 19104. Manuscript submitted June 29, 1979. METALLURGICAL TRANSACTIONS A
with the e f f e c t s of Mn and Si in conjunction with P . It i s w i d e l y r e c o g n i z e d that the a d d i t i o n of Mo in s t e e l i n h i b i t s t e m p e r e m b r i t t l e m e n t . 1-3 H o w e v e r , the m e c h a n i s m by which t h i s o c c u r s i s not y e t c l e a r . R e c e n t w o r k 4 on a N i - C r - M o s t e e l doped with 0.06 P showed that e m b r i t t l e m e n t was i n i t i a l l y s u p p r e s
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