Optimizing the boron effect
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ALTHOUGH
the role of b o r o n as a h a r d e n a b i l i t y agent has long been r e c o g n i z e d , c o n s i d e r a b l e r e s e a r c h has b e e n r e q u i r e d to d e t e r m i n e a m o u n t s of b o r o n to be added to v a r i o u s s t e e l c o m p o s i t i o n s for v a r i o u s endp r o d u c t p u r p o s e s . According to a n u m b e r of i n v e s tigations,~-7 the a m o u n t of b o r o n r e q u i r e d to p r o d u c e maximum hardenability varies considerably--from 0.00033 to 0.0025 p c t - - a n d depends on the b a s e compos i t i o n as well as other f a c t o r s . Some s t u d i e s B-~I r e ported, in p a r t i c u l a r , c a s e s where i n c r e a s i n g the b o r o n addition above c e r t a i n levels r e s u l t s in d e c r e a s e s in the h a r d e n a b i l i t y . F r o m the point of view of effective alloy design, even though t h e r e is s t i l l a lack of a g r e e m e n t in the l i t e r a t u r e about the effect of b o r o n on notch t o u g h n e s s , the use of b o r o n as a h a r d e n a b i l i t y agent should take into account the effect of this e l e m e n t on the i m p a c t p r o p e r t i e s of quenched and t e m p e r e d s t e e l s . Although the influence of a) the method of adding boron, b) the t e m p e r i n g t e m p e r a t u r e , or c) the b a s e c o m p o s i t i o n upon the effect of b o r o n on notch toughness has b e e n r e p o r t e d by m a n y i n v e s t i g a t o r s for a v a r i e t y of e x p e r i m e n t a l as well as c o m m e r c i a l s t e e l s , 8-m,12-21 no c l e a r l y d e m o n s t r a b l e e x p l a n a t i o n s of this effect have yet b e e n offered. Our r e v i e w of a v a i l a b l e l i t e r a t u r e also r e v e a l e d no s t u d i e s d e a l i n g with the effect of b o r o n on toughness of the i m p o r t a n t c l a s s of plate s t e e l s d e s i g n a t e d as ASTM A514. The p r e s e n t study, t h e r e f o r e , had a twofold p u r p o s e : 1) to a t t e m p t to d e t e r m i n e the m a n n e r in which b o r o n in e x c e s s of an o p t i m u m a m o u n t affects h a r d e n a b i l i t y and t o u g h n e s s , and 2) to e s t a b l i s h the r a n g e of b o r o n that p r o v i d e s a d e s i r a b l e c o m b i n a t i o n of h a r d e n a b i l i t y G. F. MELLOY, P. R. SLIMMON, and P. P. PODGURSKY are Manager, Supervisor, and Engineer, respectively, Alloy Development
Section, Research Department, Bethlehem Steel Corporation, Bethlehem, Pa. 18016. This paper is based on a presentation made at a sympositml on "Hardenability" held at the ClevelandMeeting of The Metallurgical Society of AIME, October 17, 1972, under the sponsorship of the IMD Heat Treatment Committee. METALLURGICAL TRANSACTIONS
and notch t o u g h n e s s for ASTM A514 Type J. This grade is a f u l l y - k i l l e d f i n e - g r a i n e d 0.12 to 0.21 C, 0.45 to 0.70 Mn, 0.50 to 0.65 Mo b o r o n - t r e a t e d s t e e l d e s i g n e d to m e e t 100,000 psi m i n i m u m yield s t r e n g t h in pla
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