Plastic anisotropy of low-carbon, low-manganese steels containing niobium
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B O T H s t e e l p r o d u c e r s and u s e r s alike have shown c o n s i d e r a b l e i n t e r e s t in r e c e n t y e a r s in improving the p r e s s f o r m a b i l i t y of low-carbon s t e e l s h e e t s . Most p r e s s forming operations used in the fabrication of components f r o m low-carbon sheets involve d e f o r m a tion by deep drawing, s t r e t c h i n g , or both. It is well known that high n o r m a l plastic anisotropy (or average p l a s t i c - s t r a i n r a t i o , r-) leads to good deep d r a w a bility ~ ,2 The use of c a r b i d e - and n i t r i d e - f o r m i n g e l e m e n t s , p a r t i c u l a r l y titanium, has been r e p o r t e d to improve the n o r m a l p l a s t i c anisotropy of l o w - c a r b o n s t e e l s h e e t s . 3'4 Other advantages of t i t a n i u m - containing s t e e l s , c o m p a r e d with r i m m e d s t e e l s , a r e a r e s i s t a n c e to s t r a i n aging and an absence of a y i e l d - p o i n t e l o n g a tion in the annealed condition (provided sufficient titanium is p r e s e n t to remove both carbon and nitrogen f r o m i n t e r s t i t i a l solid solution). E l i a s and Hook5 r e cently r e p o r t e d that excellent p l a s t i c anisotropy and f r e e d o m from s t r a i n aging were obtained for coldr o l l e d and annealed sheets of niobium-containing lowc a r b o n s t e e l s . Also, the use of niobium to form c a r bides and n i t r i d e s r a t h e r than titanium r e p o r t e d l y r e d u c e d the incidence of surface defects. 5 It has been implied in much of the previous work that the r e m o v a l of i n t e r s t i t i a l s f r o m solid solution is r e s p o n s i b l e for improved n o r m a l p l a s t i c anisotropy, and the beneficial effect of d e c a r b u r i z i n g during a n nealing on p l a s t i c anisotropy 4'6 a p p e a r s to support the i m p l i c a t i o n . S i m i l a r l y , the r e m o v a l of substitutional P. R. MOULD is Senior ResearchMetallurgist,U. S. Steel Corporation, Research Laboratory, Monroeville,Pa. 15146. J. M. GRAY, formerly with U. S. Steel Corporation, Research Laboratory, Monroeville, Pa., is now with MolybdenumCorp. of America,Pittsburgh, Pa. 15230. Manuscript submitted December 23, 1971. METALLURGICALTRANSACTIONS
e l e m e n t s such as manganese has a l s o been r e p o r t e d to i n c r e a s e n o r m a l p l a s t i c a n i s o t r o p y J A p a r t f r o m the beneficial effect of A1N p a r t i c l e s in a l u m i n u m killed s t e e l s s'9 and the d e l e t e r i o u s effects of fine i r o n oxide p a r t i c l e s ~~ on p l a s t i c anisotropy in c o l d - r o l l e d s h e e t s , little c o n s i d e r a t i o n has been given to the e f fects of p r e c i p i t a t e s on p l a s t i c a n i s o t r o p y . The purpose of the p r e s e n t work was to d e t e r m i n e the effects of niobium c a r b o n i t r i d e s , as well as of niobium in solid solution, on the p l a s t i c anisotropy of l o w - c a r b o n , low-manganese s t e e l s . Steels
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