Recrystallization behavior in deformed austenite of high strength low alloy (HSLA) steels
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High t e m p e r a t u r e d e f o r m a t i o n e x p e r i m e n t s w e r e conducted to m o n i t o r the r e c r y s t a l l i z a t i o n p r o c e s s in the a u s t e n i t e phase of a v a n a d i u m and c o l u m b i u m - t r e a t e d HSLA s t e e l alloy. Th e r e s u l t s show that c o l u m b i u m i s m u c h m o r e e f f e c t i v e than v a n a d i u m in r e t a r d i n g r e c r y s t a l l i z a t i o n . As the a u s t e n i t i z i n g t e m p e r a t u r e , above 2000~ or time is i n c r e a s e d the a u s t e n i t e r e c r y s t a l l i z a t i o n in the 1500 ~ to 1700~ hot w o r k i n g t e m p e r a t u r e range is c o r r e s p o n d i n g l y i n c r e a s e d . If, following the a u s t e n i t i z a t i o n , the s a m p l e s a r e held in the hot w o r k i n g t e m p e r a t u r e r an g e f o r up to 5 m i n b e f o r e hot w o r k i n g r e c r y s t a l l i z a t i o n o c c u r s at a much f a s t e r r a t e . S e v e r a l m e c h a n i s m s a r e o f f e r e d to e x p la in the e x p e r i m e n t a l r e s u l t s .
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r e c e n t y e a r s a c o n s i d e r a b l e e f f o r t has b e e n d ev o t e d to the d e v e l o p m e n t of s t r u c t u r a l s t e e l s with i m p r o v e d s t r e n g t h and to u g h n e s s p r o p e r t i e s . T h e s e i m p r o v e d p r o p e r t i e s have b e e n g a i n e d by u ti li zi n g p r e c i p i t a t i o n h a r d e n i n g and g r a i n r e f i n i n g m e c h a n i s m s through s e l e c t i v e alloying and c o n t r o l l e d h o t - r o l l i n g t e c h n i q u e s . C o l u m b i u m and v a n a d i u m a r e two a l l o y ing e l e m e n t s well known f o r t h e i r p r e c i p i t a t i o n h a r d ening e f f e c t s in high s t r e n g t h low a ll o y (HSLA) s t r u c t u r a l s t e e l s . They a l s o c o n t r i b u t e to the t o u g h n e s s a s well a s the s t r e n g t h by r e f i n i n g the g r a i n s i z e in both the a u s t e n i t e and f e r r i t e p h a s e s . One of the f i r s t a t t e m p t s to study the m i c r o s t r u c r u r a l a l t e r a t i o n s in i r o n and s t e e l a u s t e n i t e d u r i n g hot working was m a d e by G r a n g e . 1'2 He d e m o n s t r a t e d that a r e f i n e d a u s t e n i t e g r a i n s i z e , d e v e l o p e d during hot r o l l i n g , will r e s u l t in a f i n e r g r a i n e d t r a n s f o r m a tion product. T h i s o c c u r s b e c a u s e the g r a i n s of the t r a n s f o r m a t i o n product m o s t often n u c l e a t e at p r i o r austenite grain boundaries. Many i n v e s t i g a t o r s have s in c e d e t e r m i n e d the ef f e c t s of c o l u m b i u m and vanadium a d d it io n s on the p r o p e r t i e s of HSLA s t e e l s . 3-5 Only r e c e n t l y , howe v e r , have the m i c r o s t r u c t u r a l c h a n g e s in the a u s tenite of hot r o l l e d s t e e l s containing c o l u m b i u m , v a n a d i u m , and a l u m i n u m b e e n studied. Kozasu and Kubota 6 have shown a s t r o n g s
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