Transformation characteristics of low-carbon steels containing 5 Pct Ni
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T H E R E has been c o n s i d e r a b l e i n t e r e s t r e c e n t l y in the use of l o w - c a r b o n s t e e l s for h i g h - s t r e n g t h s t r u c t u r a l a p p l i c a t i o n s . The b e n e f i t s that m a y be d e r i v e d from the use of these s t e e l s a r e i n c r e a s e d toughness and i m p r o v e d weldability. High s t r e n g t h s have b e e n obtained in l o w - c a r b o n s t e e l s c o n t a i n i n g s m a l l additions of alloying e l e m e n t s in both the h o t - r o l l e d 1. and the *See References. quenched and t e m p e r e d 2 conditions. Studies d i r e c t e d toward the development of l o w - c a r b o n s t e e l s have e m p h a s i z e d the i m p o r t a n c e of the t r a n s f o r m a t i o n product and its a s s o c i a t e d s u b s t r u c t u r e in d e t e r m i n i n g the m e c h a n i c a l p r o p e r t i e s . A wide r a n g e of s t r u c t u r e s m a y be obtained on quenching these s t e e l s from the a u s t e n i t i c condition, but most of the s t r u c t u r e s a r e not well documented. C o n s e q u e n t l y , the u n d e r s t a n d i n g and c h a r a c t e r i z a t i o n of the t r a n s f o r m a t i o n s and their r e s u l t i n g s t r u c t u r e s should aid in the d e v e l o p m e n t of new l o w - c a r b o n s t e e l s . An e a r l i e r paper 3 d e s c r i b e d the s t r u c t u r e and c r y s t a l l o g r a p h i c f e a t u r e s of the m a r t e n s i t e t r a n s f o r m a t i o n . The p r e s e n t p a p e r is c o n c e r n e d p r i m a r i l y with t r a n s f o r m a t i o n s that occur at t e m p e r a t u r e s above the m a r t e n s i t e t r a n s f o r m a t i o n temperature. I s o t h e r m a l t r a n s f o r m a t i o n s t u d i e s have b e e n used e x t e n s i v e l y to e x a m i n e the influence of t r a n s f o r m a t i o n t e m p e r a t u r e on the n a t u r e of a u s t e n i t e d e c o m p o s i t i o n products. 4 However, v e r y little data exist for s t e e l s c o n t a i n i n g l e s s than 0.2 pct C . s - " The r e a s o n for this lack of i n f o r m a t i o n is that the t r a n s f o r m a t i o n to polygonal f e r r i t e o c c u r s so r a p i d l y in these m a t e r i a l s at about 600~ that, even with f a i r l y high cooling r a t e s , it i s difficult to s u p p r e s s this t r a n s f o r m a t i o n to e x a m i n e s t r u c t u r e s f o r m e d at lower t e m p e r a t u r e s . 9 F o r the s a m e r e a s o n , little i n f o r m a t i o n e x i s t s c o n c e r n i n g continuous cooling t r a n s f o r m a t i o n s in these m a t e r i a l s . In the p r e s e n t i n v e s t i g a t i o n an a t t e m p t was made to o v e r c o m e some of these difficulties by adding 4 to 5 pct Ni to the s t e e l s e x a m i n e d and a l s o by using thin J. M. CHILTON, formerly with the Applied Research Laboratory, U. S. Steel Corp., Monroeville,Pa., is presently with Bell Telephone Laboratories, Allentown, Pa. G. R. SPEICHis with the Edgar C. Bain La
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