A study of the delamination behavior of a very low-carbon steel
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L A M I N A T E D f r a c t u r e in Charpy and t e n s i l e s p e c i m e n s of h i g h - s t r e n g t h low alloy s t e e l has b e c o m e an i n c r e a s i n g c o n c e r n in r e c e n t y e a r s b e c a u s e of the c r i t i c a l application of these m a t e r i a l s . L a m i n a t i o n s , o r s p l i t s , o c c u r p a r a l l e l to the r o l l i n g plane in plate f i n i s h e d below the A1 t e m p e r a t u r e . In a d i s c u s s i o n of a r e c e n t paper, 1 a m e c h a n i s m for the cause of l a m i n a t e d f r a c t u r e was proposed. T h e f r a c t u r e b e h a v i o r was r e l a t e d to the i n t r o d u c t i o n of a s u b s t a n t i a l a m o u n t of d e f o r m e d f e r r i t e in the m i c r o s t r u c t u r e , thus p r o d u c i n g a plane of w e a k n e s s a l i g n e d p a r a l l e l to the r o l l i n g plane. The f r a c t u r e , which was not a s s o c i a t e d with a s t r o n g (100) t e x t u r e o r n o n m e t a l l i c i n c l u s i o n s , did not have a c l a s s i c cleavage a p p e a r a n c e but o c c u r r e d as a t e a r i n g phen o m e n o n a s s o c i a t e d with c o n s i d e r a b l e n e c k i n g and ductility. Many p a p e r s have r e l a t e d the d e l a m i n a t i o n phen o m e n o n in s t e e l s to g r a i n - b o u n d a r y f a i l u r e , ~-~ the d i s t r i b u t i o n and morphology of c a r b i d e s , ~-~ or c l e a vage along (100) p l a n e s . 7-1~ Lentz n p r o p o s e d a mode f o r s p l i t t i n g f r a c t u r e b a s e d on a m e c h a n i c a l f i b e r i n g t h e o r y and was able to r e p r o d u c e the s p l i t t i n g f r a c t u r e i n a w a r m r o l l e d a l u m i n u m alloy. All of the above i n v e s t i g a t i o n s were made on 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 e i t h e r p r e c i p i t a t e s or second phases such as p e a r l i t e and b a i n i t e . U s i n g a h i g h - p u r i t y F e - 1 pet Mn alloy without second p h a s e s to c o m p l i c a t e the a n a l y s i s , the p u r p o s e of the p r e s e n t study was to f u r t h e r c h a r a c t e r i z e the l a m i n a t e d f r a c t u r e and d e t e r m i n e the m i c r o s t r u c t u r a l f e a t u r e r e s p o n s i b l e for this phenomenon.
EXPERIMENTAL
PROCEDURE
A vacuum-induction melted, high-purity Fe-I pct Mn alloy (Table I) was selected for this study to eliminate the undesirable factors of sulfide inclusions, pearlite, pearlite banding, nitrides, and grainboundary carbides, Four 225 kg ingots were rolled into sixteen I00 mm 2 slabs, which were then reheated
B. L. BRAMFITTand A. R. MARDER are associated with Research Department, Bethlehem Steel Corporation, Bethlehem. PA 18016. Manuscript submitted September 13, 1976. METALLURGICALTRANSACTIONSA
to 1100 to 1250~ for 2 h and rolled into 12.7 mm thick plate in ten p a s s e s ) Finishing temperatures varied from 960 down to 150~ and both plate surface temperature and mill load were measured for all passes. After mechanical testing
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