Prediction of alloy hardenability from thermodynamic and kinetic data
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t i o n s for t e r n a r y and higher alloy F e - C b a s e d s y s t e m s . The a c c o m p a n y i n g e x p e r i m e n t a l p a p e r by B r a m f i t t and M a r d e r 6 e p i t o m i z e s the p r e c i s e data for s t e e l s of w e l l defined c h e m i s t r y which is b e c o m i n g i n c r e a s i n g l y a v a i l able. Phase d i a g r a m s , n u c l e a t i o n r a t e , and p e a r l i t e v e l o c i t y vs t e m p e r a t u r e c u r v e s , TTT, CCT, and h a r d e n a b i l i t y c u r v e s a r e now being g e n e r a t e d for m a n y highp u r i t y b a s e F e - C - X s y s t e m s . Along with f u n d a m e n t a l diffusion data, such e x p e r i m e n t a l m a t e r i a l is g r i s t for the c o r r e l a t o r ' s m i l l . The following s y n t h e s i s of t h e o r y with o b s e r v a t i o n s of n u c l e a t i o n , growth, and heat t r a n s f e r p r o c e s s e s is a i m e d at the p r e d i c t i o n of the r e s u l t s of an e n d - q u e n c h test.
PROCEDURE FOR CALCULATION OF HARDENABILITY We r e s t r i c t o u r s e l v e s in this p a p e r to the c a l c u l a t i o n of the h a r d e n a b i l i t y of low alloy eutectoid s t e e l s so that the c a r b o n content may, to the f i r s t a p p r o x i m a t i o n , be taken as fixed. With G r o s s m a n 7 we a s s u m e an ideal (infinitely s e v e r e ) quench and for p u r p o s e s of n u m e r i cal c a l c u l a t i o n c o n s i d e r alloys which a r e c o m p l e t e l y homogenized at a soaking t e m p e r a t u r e of 860~ 3 and i d e a l l y e n d - q u e n c h e d at a t e m p e r a t u r e of 100~ It is a s s u m e d : that f r o m t h e r m o d y n a m i c s we a r e given an e x p r e s s i o n for the effective eutectoid t e m p e r a t u r e as a function of c o m p o s i t i o n ; that f r o m n u c l e a t i o n t h e o r y we a r e given an e x p r e s s i o n for the i n c u b a t i o n t i m e ( T T T s t a r t c u r v e s ) as a function of u n d e r c o o l i n g and c o m p o s i t i o n ; that we a r e given a p r o c e d u r e for c o n v e r t ing a T T T c u r v e to a CCT c u r v e ; that we a r e given the g r a i n size and a r e a l i s t i c model for a s i t e - s a t u r a t e d d i s t r i b u t i o n of p e a r l i t e nuclei at the end of the i n c u b a tion t i m e ; and that we a r e given an e x p r e s s i o n for the p e a r l i t e growth v e l o c i t y as a function of c o m p o s i t i o n VOLUME 4, OCTOBER 1973-2327
and t e m p e r a t u r e . The a l g o r i t h m , t h e r e f o r e , p r o c e e d s as follows : 1) Calculate the cooling c u r v e s for a r e p r e s e n t a t i v e set of depths in the J o m i n y b a r , using the t i m e - d e p e n dent F o u r i e r equation for heat conduction. 2) T r a n s f o r m the t i m e axis of the cooling c u r v e s so that the t i m e z e r o of each c u r v e c o r r e s p o n d s to the alloy eutectoid t e m p e r a t u r e . 3) C a l c u l a t e the i n c u b a t i o n t i m e ( T T T s t a r t curve) as
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