Sulfide inclusions in steel
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EXPERIMENTAL
l o s s of v o l a t i l e e l e m e n t s b e g a n to i n c r e a s e around 1200~ the f u r n a c e was b a c ~ i l l e d with o n e - h a l f an a t m o s p h e r e of h e l i u m to m i n i m i z e these l o s s e s . When a e a r b o n - d e o x i d a t i o n was r e q u i r e d , it was p e r f o r m e d by pumping back down to 1000 m i c r o n s to obtain a boil, then b a c k - f i l l i n g again d u r i n g s o l i d i f i c a t i o n . V a r i o u s cooling r a t e s f r o m 0 . 1 ~ to 100~ w e r e obtained by cooling with r e d u c e d induction power, by lifting the c r u c i b l e out of the s u s c e p t o r , o r by touching the s u r face of the m e l t with a w a t e r cooled i r o n tube. T e m p e r a t u r e was m e a s u r e d by m e a n s of a p l a t i n u m - p l a t i n u m / 1 0 p et r h o d i u m t h e r m o c o u p l e which was p r o t e c t e d by an a l u m i n a tube and i n s e r t e d into the m e l t . T e m p e r a t u r e was continuously m o n i t o r e d and r e c o r d e d on a strip chart. TH E F e - M n - S PHASE DIAGRAM The F e - M n - S s y s t e m has b e e n defined in the l i t e r a t a r e in its g e n e r a l outline, but t h e r e is d i s a g r e e m e n t on s o m e d e t a i l s , and a l m o s t no f i r m d a t a which can be used f o r q u a n t i t a t i v e s t u d i e s . ~3-z8 The i m p o r t a n t p o r tion of the p h ase d i a g r a m in the i r o n c o r n e r was i n v e s tigated to p r o v i d e m o r e d e t a i l e d i n f o r m a t i o n . The c o m positions of s p e c i m e n s used f o r the p h ase d i a g r a m and m o r p h o l o g i c a l st u d i es a r e g i v en in T a b l e s I and II. D e oxidation of the m e l t was a c c o m p l i s h e d e i t h e r by a c a r b o n - b o i l , o r by the addition of a l u m i n u m in o r d e r to d e t e r m i n e w h e t h e r changes in s o l i d i f i c a t i o n b e h a v i o r o r su l f i d e m o r p h o l o g y would r e s u l t . No changes were observed. Fig. 1 shows the liquidus i s o t h e r m s in the i r o n c o r n e r of the F e - M n - S s y s t e m . The i s o t h e r m s w e r e d e r i v e d f r o m the s o l i d i f i c a t i o n c u r v e s of s o m e of the
PROCEDURE
The e x p e r i m e n t a l a l l o y s w e r e made and s o l i d i f i e d in a v a c u u m induction f u r n a c e , using high p u r i t y a l u m i n a c r u c i b l e s . The ingots r a n g e d in s i z e f r o m 50 to 500 g r a m s . High p u r i t y m a t e r i a l s , such as " F e r r o v a c - E " iron, w e r e used throughout. Additions of m a s t e r a l l o y s containing m a n g a n e s e , carbon, and the o t h e r e l e m e n t s w e r e m a d e d i r e c t l y to the m e l t in the c r u c i b l e , u s u a l l y at 1650~ During i n i t i a l heating a v a c u u m of o n e - t e n t h of a m i c r o n was used. When the L. K. BIGELOWis Program Manager, Ledgemont Laboratory, Kennecott Copper Corp., Lexington, Mass. M.C. FLEMINGS is Abex Professor of Metallurgy, Department of Me
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