Strengthening of steel by the method of spraying oxide particles into molten steel stream
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I. INTRODUCTION
IT is previously known that nonmetallic inclusions
in a commercial steel have a large effect on its workability and toughness by their size, morphology and distribution. According to the theory of dispersions t r e n g t h e n i n g , s t r e n g t h i n c r e a s e s with the v o l u m e f r a c t i o n of fine d i s p e r s e d p a r t i c l e s in m a t e r i a l , z,2 T h i s m a y s u g g e s t that it is p o s s i b l e to i n c r e a s e the s t r e n g t h of s t e e l by h o m o g e n e o u s d i s p e r s i o n of fine n o n m e t a l l i c i n c l u s i o n s in s t e e l . Although d i s p e r s i o n - s t r e n g t h e n e d a l l o y s , s u c h as SAP of a l u m i n u m a ll o y or T D - n i c k e l , have b e e n widely d e v e l o p e d , they a r e p r o d u c e d by the m e t h o d of s u r f a c e oxidation, c o p r e c i p i t a t i o n or p o w d e r m e t a l l u r g y , and t h e r e is l i t t l e i n f o r m a t i o n on a c a s t i n g m e t h o d of d i s p e r s i o n - s t r e n g t h e n e d alloy. A s a new t e c h n i q u e , S p r a y - D i s p e r s i o n Method*, 3"~ *Japanese Patent, pending. w as d e v e l o p e d w h e r e oxide p o w d e r s a r e s p r a y e d f r o m o u t s i d e into m o l t e n s t e e l s t r e a m c o n t a i n i n g a s m a l l a m o u n t of a s u i t a b l e d i s t r i b u t i o n - c o n t r o l l i n g e l e m e n t . The possibility for porducing d i s p e r s i o n - s t r e n g t h e n e d s t e e l by this m e t h o d was i n v e s t i g a t e d by the a u t h o r s , and s o m e r e s u l t s of i n t e r e s t a r e r e p o r t e d in t h i s paper.
w as added. U s i n g a p l a s m a - s p r a y p o w d e r f e e d e r , oxide p o w d e r was then s p r a y e d into the s t e e l s t r e a m d u r i n g p o u r i n g into an ingot with a r g o n gas p r e s s u r i z e d below 1 M P a . TiO2, A1203, ZrO2 or CeO2 p o w d e r was s e l e c t e d as s p r a y i n g oxide. T h e a v e r a g e p a r t i c l e s i z e m e a s u r e m e n t s w e r e m a d e by the B l a i n e ' s method; 6 the r e s u l t s a r e shown in T a b l e I. T h e c o n t r o l l i n g e l e ment, s u c h as v a n a d i u m , c h r o m i u m , n i c k e l , c o l u m b i u m , m o l y b d e n u m , and so forth, which changed t h e s u r f a c e t e n s i o n of m o l t e n s t e e l and the i n t e r r a c i a l t e n s i o n at the o x i d e - m o l t e n s t e e l i n t e r f a c e , was added in s t e e l . T h e i n g o t s w e r e h o m o g e n i z e d at 1273 K f o r 5 h f o l lowed by hot w o r k i n g at 1273 K (the r a t i o of hot w o r k ing: 15 the f i n al s i z e : 15 x 15 x 1700 m m ) , and s p e c i -
Table I, Average Size of Oxide Powders Measured by Blaine's Method
OxidePowder
AverageSize,/~m
TiO2 A120a ZrO2 CeO2
8 11 9 10
Table II. Chemical Composition of Specimens and Average Particle Size, Average Planar Interparticle Spacing and Volume Fraction of Oxide Particles
II. E X P E R I M E N T A L P R O C E D U R E S 1. M a t
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