High strength low carbon sheet steel by thermomechanical treatment: l. Strengthening mechanisms
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s t r e n g t h r e q u i r e m e n t s of a u t o m o t i v e c o m p o n e n t s f a b r i c a t e d b y s t a m p i n g a r e m e t by s p e c i f y i n g the y i e l d s t r e n g t h of the a s - r e c e i v e d s h e e t m e t a l . T h i s a p p r o a c h i g n o r e s both the i n c r e a s e in flow s t r e s s due to w o r k h a r d e n i n g d u r i n g f o r m i n g and the i n c r e a s e due to age h a r d e n i n g which m a y o c c u r a f t e r f o r m i n g . T h e s e c o n t r i b u t i o n s to s t r e n g t h a r e d i s c o u n t e d b e c a u s e m a n y a r e a s of p r o d u c t i o n s t a m p i n g s e x p e r i e n c e only l i m i t e d d e f o r m a t i o n , and a p p r e c i a b l e s t r e n g t h e n i n g by e i t h e r of t h e s e m e c h a n i s m s u s u a l l y r e q u i r e s s i g n i f i c a n t (>5 pct) d e f o r m a tion. D e s p i t e t h e s e p r o b l e m s the c o n c e p t of u t i l i z i n g the s t r e n g t h d e v e l o p e d d u r i n g the f o r m i n g o p e r a t i o n in the s t r e n g t h s p e c i f i c a t i o n r e m a i n s a t t r a c t i v e . It is c l e a r h o w e v e r that to t a k e full a d v a n t a g e of this s t r e n g t h i n c r e a s e , a new m a t e r i a l is r e q u i r e d to o v e r c o m e the d i s a d v a n t a g e s c i t e d a b o v e . The above c o n s i d e r a t i o n s coupled with the i n c r e a s ing r e q u i r e m e n t s f o r h i g h e r s t r e n g t h s t e e l s in a u t o m o t i v e s t r u c t u r e s p r o m p t e d the d e v e l o p m e n t of T M T 550, a s t e e l which would d e v e l o p a m i n i m u m y i e l d s t r e n g t h of 550 M P a (80 ksi) in the s t a m p i n g a f t e r m i n i m a l d e f o r m a t i o n . C l e a r l y a p r o d u c t at t h i s s t r e n g t h l e v e l m u s t c o m p e t e with the m o r e convent i o n a l m i c r o a l l o y e d high s t r e n g t h s t e e l s with 550 M P a y i e l d s t r e n g t h and thus a s e c o n d r e q u i r e m e n t was e s t a b l i s h e d - t h e f o r m a b i l i t y of TMT 550 should be c o m p a r a b l e to that of 980 High S t r e n g t h Low A l l o y (HSLA) s t e e l s . T h e goal of t h i s i n v e s t i g a t i o n then was to develop a material exhibiting a minimum tensile e l o n g a t i o n of 18 pct p r i o r to d e f o r m a t i o n , and a DONALD J. BAILEY, formerly with the Physics Department, General Motors Research Laboratories is now with General Electric Company, Nuclear Energy Division, San Jose, CA 95125. ROBIN STEVENSON is with the Physics Department, General Motors Research Laboratories, Warren, M148090. Manuscript submitted June 16, 1977. METALLURGICAL TRANSACTIONS A
m i n i m u m y i e l d s t r e n g t h of 550 M P a (80 ksi) a f t e r d e f o r m a t i o n and aging. TMT Concept In d e v e l o p i n g a s t e e l to t a k e a d v a n t a g e of the f o r m ing o p e r a t i o n a s a s t r e n g t h e n i n g m e c h a n i s m , the a p p r o a c h a d o p t e d was to modify the m
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