Effect of cooling rate and alloying on the
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AND
A. R. MARDER
The p e a r l i t i c h a r d e n a b i l i t y of a h i g h - p u r i t y F e - 0 . 8 p c t C a l l o y and z o n e - r e f i n e d i r o n b i n a r y a l l o y s c o n t a i n i n g Mn, Ni, Si, Mo, o r Co was s t u d i e d b y m e a n s of h o t - s t a g e m i c r o s c o p y . The b i n a r y a l l o y s w e r e c a r b u r i z e d in a g r a d i e n t f u r n a c e to p r o d u c e e u t e c t o i d c o m p o s i t i o n s , thus e l i m i n a t i n g p r o e u t e c t o i d p h a s e s . A s p e c i a l technique b a s e d on h o t - s t a g e m i c r o s c o p y was u s e d to s t u d y the effect of c o o l i n g r a t e ( 1 0 ~ to 25,000~ on the t r a n s f o r m a t i o n of a u s t e n i t e and p r o v i d e d d a t a for the c o n s t r u c t i o n of continuous c o o l i n g - t r a n s f o r m a t i o n d i a g r a m s . F r o m t h e s e d i a g r a m s c r i t i c a l c o o l i n g r a t e s w e r e o b t a i n e d for h a r d e n a b i l i t y c a l c u l a t i o n s . It was found that m o l y b d e n u m is the m o s t e f f e c t i v e e l e m e n t , followed b y Si, Ni. Co, and Mn, in s u p p r e s s i n g the p e a r l i t e t r a n s f o r m a t i o n , i.e., in i n c r e a s i n g the h a r d e n a b i l i t y of the a l l o y s s t u d i e d . The a l l o y i n g a d d i t i o n s w e r e g r o u p e d into two c l a s s e s a c c o r d i n g to t h e i r effect on h a r d e n a b i l i t y : a - s t a b i l i z e r s (Mo and Si) and v - s t a b i l i z e r s (Ni, Co, Mn), with the a - s t a b i l i z e r s b e i n g the m o r e e f f e c t i v e in i m p r o v i n g h a r d e n a b i l i t y .
LONG
a w a r e of the c o m m e r c i a l i m p o r t a n c e of h a r d e n a b i l i t y , m e t a l l u r g i s t s have o v e r the y e a r s been s t u d y ing the c o m p o s i t i o n a l and m i c r o s t r u c t u r a l f a c t o r s a f f e c t i n g h a r d e n a b i l i t y in o r d e r to d e v e l o p a l l o y d e s i g n c r i t e r i a , p a r t i c u l a r l y for m o d e r n h i g h - s t r e n g t h a p p l i c a t i o n s . F o r e x a m p l e , p a r t l y b e c a u s e of the s t i m u l u s of the p r o p e r t y r e q u i r e m e n t s f o r new s t e e l s f o r s h i p s , a i r c r a f t , and o r d n a n c e in the e a r l y 1940's, G r o s s m a n , 1 followed b y o t h e r s , 2-4 d e v e l o p e d s o m e of the b a s i c quant i t a t i v e d a t a for such a l l o y d e s i g n n e e d s . T h e i r w o r k a l l o w e d m e t a l l u r g i s t s to a p p r o x i m a t e the " i d e a l c r i t i c a l d i a m e t e r " of a s t e e l b a r by using m u l t i p l y i n g f a c t o r s for c h e m i c a l c o m p o s i t i o n and g r a i n s i z e . Many s t e e l s w e r e s u b s e q u e n t l y d e s i g n e d using t h i s b a s i c d a t a f o r h a r d e n a b t l i t y c a l c u l a t i o n s , d a t a which is s t i l l in wide use today. F u n d a m e n t a l to the p r o b l e m s of d e s i g n i n g a l l o y s for o p t i m u m h
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