The extent and nature of the strength-differential effect in steels
- PDF / 3,688,625 Bytes
- 13 Pages / 612 x 792 pts (letter) Page_size
- 35 Downloads / 145 Views
M A R T E N S I T I C s t e e l s y i e l d at h i g h e r s t r e s s e s when t e s t e d in u n i a x i a l c o m p r e s s i o n than when t e s t e d in t e n s i o n . This p h e n o m e n o n , which was e n c o u n t e r e d but not s p e c i f i c a l l y i n v e s t i g a t e d by s e v e r a l p r e v i o u s w o r k e r s , 1-3 was m o r e r e c e n t l y o b s e r v e d by L e s l i e and S o b er 4 in t h e i r study of m a r t e n s i t e s t r e n g t h , in which they c o m p a r e d the r e s u l t s of te n s i o n and c o m p r e s s i o n t e s t s for s e v e r a l a l l o y s and heat t r e a t m e n t s . In a s u b s e q u e n t study, K a l i s h and Cohen 5 a l s o found a s t r e n g t h d i f f e r e n c e . T h e p u r p o s e of the w o r k to be d e s c r i b e d h e r e is to e s t a b l i s h the extent and n a t u r e of this s t r e n g t h d i f f e r e n t i a l , now known as the " S D " e ff ect . PR~, VIOUS WORK
Metals are usually assumed to have equal yield and flow stresses in tension and compression. This as-sumption is often based primarily on mathematical convenience,and there are indeed exceptions to this rule; for example, Bauschinger6 found in 1886 that in unidirectionally prestrained steels tensile and compressive yield strengths were not equal. In the absence of such factors as the Bauschinger effect, however, tension and compression tests on many different metals and alloys have shown no strength differential at plastic strains as high as 80 pct.TM On the other hand, as early as 1927 Siebel and Pomp~ found that steels, even in the fully annealed condition,behaved differently, the flow stress in compression being significantly h i g h e r than in t e n s i o n . S i m i l a r r e s u l t s w e r e r e p o r t e d in 1951 by P o l a k o w s k i . 3 Although the e a r l y w o r k dealt p r i m a r i l y with s t e e l s having a s h a r p y i e l d point, m o s t of the e a r l y p a p e r s , and o t h e r s m o r e r e c e n t , 9 p r e s e n t no data f o r p l a s t i c s t r a i n s in the Lf i d er s d e f o r m a t i o n r a n g e , so that it is not p o s s i b l e to d e t e r m i n e w h e t h e r a s t r e n g t h d i f f e r e n c e was p r e s e n t at the l o w e r y i el d s t r e s s . T h e Lfiders s t r a i n is g e n e r a l l y s m a l l e r in a c o m p r e s s i o n t e s t than in a t e n s i l e t e s t , so that a c o m p r e s s i o n s p e c i m e n s t a r t s to w o r k - h a r d e n at l o w e r s t r a i n s than does a t e n s i l e s p e c i m e n . 1~ T h u s , G. C. RAUC~I,formerly with E. C. Bain Laboratory for Fundamental Research, United States Steel Corporation, is now with Magnetics Department, Westinghouse Research Laboratories, Pittsburgh, Pa. W. C. LESLIE is with E. C. Bain Laboratory for Fundamental Research, United States Steel Corporation, Research Center, Monroeville, Pa. Manuscript submitted April 16, 1971. METALLURGICALTRANSACTIONS
t h e r e i s an a p p a r e n t SD e f f e c t in the flow stress, but not n e c e s
Data Loading...
