The influence of boron upon r m value in aluminum killed drawing quality steel
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is well e s t a b l i s h e d that the s u p e r i o r drawing p r o p e r t i e s of c o m m e r c i a l alufninum-killed s t e e l d e r i v e s f r o m the p r o p e r development of t e x t u r e during r e c r y s t a l l i z a t i o n which in turn depends c r i t i c a l l y on the cont r o l of A1N p r e c i p i t a t i o n in p r o c e s s i n g . The b a s i c r e q u i r e m e n t is to r e t a i n aluminum and nitrogen in s o l u tion a f t e r hot d e f o r m a t i o n and p r i o r to cold reduction such that these e l e m e n t s a r e available for " p r e p r e c i p i t a t i o n c l u s t e r i n g " at subgrain o r p r i o r c o l d worked g r a i n b o u n d a r i e s during the subsequent anneal. This a p p a r e n t l y induces the p r e f e r e n t i a l nucleation and growth of {111} g r a i n s p a r a l l e l to the sheet plane which r e s u l t s in high r m value and good drawing p r o p e r t i e s . A number of s t u d i e s have shown that if A1N is p r e c i p i tated p r i o r to cold reduction, the {111} texture d e v e l opment is p r e v e n t e d such that the d r a w a b i l i t y p r o p e r t i e s a r e reduced to that of r i m m e d s t e e l . 1-a It is apparent that the d e s i r e d e f f e c t s of A1N p r e c i p i tation may be nullified by f a c t o r s such as the p r e s e n c e of i m p u r i t y e l e m e n t s . Boron is one such e l e m e n t and can be introduced into continuously e a s t s t e e l s when a flux containing boron oxide is used to l u b r i c a t e the mold during casting. ~ Although it is known that boron e x e r t s b e n e f i c i a l effects on the h a r d e n a b i l i t y of s t e e l s S it will be shown in this investigation that only a v e r y s m a l l amount of boron i s n e c e s s a r y to produce a p r o nounced d e t e r i o r a t i o n in the t e x t u r e development of high r m values in c o m m e r c i a l a l u m i n u m - k i l l e d steeI, an effect which will be explained in t e r m s of an effective s u p p r e s s i o n of the r e q u i s i t e AIN p r e c i p i t a t i o n during t h e final anneal. MATERIALS .AND EXPERIMENTAL PROCEDURES Low l e v e l s of boron in the range 0 to 50 ppm w e r e introduced into four conventionally c a s t aluminum killed s t e e l ingots by the use of f e r r o b o r o n additions during teeming. A 12.9 Mg* d i s p o s a b l e hot top mold was used *Sl symbolfor megagram---0.907 to~s. and the a p p r o p r i a t e f e r r o b o r o n a d d i t i v e s w e r e added to 1/4 to 2/3 ingot height~ The four boron b e a r i n g ingots together with a r e g u l a r aluminum killed ingot as r e f e r enee w e r e r o i l e d into slabs 940 m m wide • 234 mm thick~ The five s l a b s w e r e hot r o l l e d into 2~ mm thick D. T. QUINTO and I. F, HUGHES are Research Engineer and Assistant Director, respectively,Inland Steel Research Laboratories, East Chicago, IN 46312. Manuscript submitted June 11, 1974. METALLURGICALTRANSACTIONSA
c o i l s using finishing t e m p e r a t u r e s in the r a
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