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T H E c o m p a n y in which the w r i t e r is e m p l o y e d is chiefly known as a m a n u f a c t u r e r of high quality t a p e r e d r o l l e r b e a r i n g s which a r e made f r o m c a r b u r i z i n g s t e e l s . However, it has for m a n y y e a r s also b e e n a p r i m e s u p p l i e r of high c a r b o n alloy s t e e l s and c a r b u r i z i n g g r a d e s to the b e a r i n g , g e a r , and tool s t e e l i n d u s t r i e s . In such p r o d u c t s , the a i m is always to m a x i m i z e load c a r r y i n g capacity, t o u g h n e s s and fatigue r e s i s t a n c e . C o n s e quently, a g e n e r a l r e q u i r e m e n t is a fully m a r t e n s i t i c s t r u c t u r e (or m a r t e n s i t e with an o p t i m u m a m o u n t of r e t a i n e d a u s t e n i t e ) f r e e of the t r a n s f o r m a t i o n p r o d u c t s p e a r l i t e , b a i n i t e , or p r o e u t e c t o i d f e r r i t e . This s t r u c t u r e m a y be d e s i r e d throughout the e n t i r e c r o s s - s e c t i o n of the p a r t or tool or s i m p l y to s o m e depth f r o m the s u r f a c e . It is obvious f r o m t h e s e c o n s i d e r a t i o n s that the s u b j e c t of h a r d e n a b i l i t y and e s p e c i a l l y h a r d e n a b i l i t y c o n t r o l at high c a r b o n l e v e l s has always b e e n of g r e a t i m p o r t a n c e to our c o m p a n y and to the w r i t e r . Indeed, at t i m e s the m a t t e r took on c r i t i c a l s i g n i f i c a n c e , s i n c e at l e a s t t h r e e p e r i o d s of c u r t a i l m e n t or bonafide s h o r t ages of n i c k e l , m o l y b d e n u m , and other e l e m e n t s i m p o r tant to our p r o d u c t had to be dealt with in the past twenty y e a r s to a s s u r e a p r o d u c t of p r o p e r h a r d e n ability. BACKGROUND OF PREVIOUS HARDENABILITY RESEARCH IN HIGH CARBON STEELS The work d e s c r i b e d h e r e i n is l a r g e l y an addition to and an u p g r a d i n g of h a r d e n a b i l i t y data p r e s e n t e d in t h r e e p r e v i o u s p a p e r s w r i t t e n by the author which w e r e c o n c e r n e d with the c a l c u l a t i o n and c o n t r o l of h a r d e n a b i l i t y at high c a r b o n l e v e l s , t-4 In all t h r e e i n s t a n c e s , the G r o s s m a n n 5 s y s t e m for c h a r a c t e r i z i n g h a r d e n a b i l ity in t e r m s of D I - t h e ideal c r i t i c a l d i a m e t e r - - w a s e m p l o y e d to e s t a b l i s h the specific h a r d e n a b i l i t y effects of m a n g a n e s e , s i l i c o r b c h r o m i u m , nickel, m o l y b d e n u m , C. F. JATCZAKis Section Chief, Physical Metallurgy Research, The Timken Company, Canton, Ohio 44706. This paper is based on a presentation made at a symposium on "Hardenability" held at the Cleveland Meeting of The MetallurgicalSociety of AIME, October 17, 1972, under the sponsorship of the IMD Heat Treatment Committee. METALLURGICALTRANSACTIONS

and b o r o n at c a r b o n l e v e l s r a n g i n g f r o m roughly 0.75