Elastic constants of martensite
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knowledge of the effects of carbon and substitutional alloying elements on the elastic constants of martensite is required for an understanding of the strength of this material. The earlier extensive work of Schmidtmann et al. ~ supported by our own studies z indicates that carbon decreases Young's modulus of Fe-C martenslte. Therefore, the recent claim by Dey e t a l . s that carbon i n c r e a s e s Young's modulus, the s h e a r modulus, and the bulk modulus of F e - N t - C m a r t e n s i t e c o n t r a d i c t s both our work and that of Schmidtmann. Dey e t a l . a l s o contend that the i n c r e a s e d e l a s t i c stiffness of the l a t t i c e caused by c a r bon additions can account for the strength of m a r t e n site. I n t e r p r e t a t i o n of the work of Dey et al. s is c o m p l i cated s e v e r e l y by t h e i r simultaneous v a r i a t i o n of the carbon and nickel contents of t h e i r m a r t e n s t t e s , inc r e a s i n g c a r b o n while d e c r e a s i n g nickel. Nickel d r a s t i c a l l y d e c r e a s e s the e l a s t i c constants of iron; z'4-6 t h e r e f o r e , t h e i r o b s e r v e d i n c r e a s e of e l a s t i c constants with i n c r e a s e d c a r b o n content may r e f l e c t s i m p l y the concomitant d e c r e a s e of nickel content. In addition, high-nlckel, h i g h - c a r b o n s t e e l s (10.8 pct Nl, 0.92 pct C) will contain significant amounts of r e t a i n e d a u s t e n ite even a f t e r quenching in liquid nitrogen. Retained austenlte is p r e s e n t even in b i n a r y F e - C a l l o y s of these carbon contents, s i m i l a r l y t r e a t e d . 7 Such r e tained austenite will affect both the d e n s i t y and the wave v e l o c i t i e s used in the calculation of the e l a s t i c constants. In the p r e s e n t work, Young's modulus (E) and the s h e a r modulus (G) have been m e a s u r e d for a s e r i e s of F e - N i alloys and of two F e - N i - C a l l o y s . The l a t t e r two a l l o y s a r e s i m i l a r to two studied by Dey e t a l . s In addition, the F e - N i - C a l l o y s w e r e p r e p a r e d with v a r i o u s amounts of austentte by quenching to v a r i o u s t e m p e r a t u r e s below room t e m p e r a t u r e . With these data it is p o s s i b l e to c o r r e c t the e l a s t i c - c o n s t a n t data for both v a r y i n g nickel and r e t a i n e d austenite contents and to m e a s u r e the t r u e effect of carbon on the e l a s t i c constants of F e - N t - C m a r t e n s i t e . EXPERIMENTAL PROCEDURE AND RESULTS The c h e m i c a l compositions of the a l l o y s used in this study a r e given in Table I. All the a l l o y s w e r e v a c u u m G. R. SPEICH is Senior Scientist, Research Laboratory, United States Steel Corporation, Monroeviile, Pa. 15146. W. C. LESLIE is Professor, Department of Materials and Metallurgical Engineering, University of Michigan, Ann Arbor, Mich. 48104 Manuscript submitted April 3, 1973. METALLURGICAL TRANSACTIONS
melted and h o t - r o l l e d
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