Accession Number : AD0614447

Title :   THE ROLE OF CARBON AND FINE STRUCTURE IN THE HARDENING OF IRON-NICKEL-CARBON MARTENSITES,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF METALLURGY AND MATERIALS SCIENCE

Personal Author(s) : Richman,Marc H. ; Cohen,Morris

Report Date : 27 APR 1965

Pagination or Media Count : 32

Abstract : The internal twins in iron-nickel and iron-nickel-carbon martensites have been measured by transmission electron microscopy under a number of conditions. The mean twin thickness is 57 = 5 A, and the mean twin spacing is 97 = 5 A, independent of the carbon content, M sub s temperature, and whether the martensite is formed athermally or isothermally (by electrolytic thinning of the specimen). The ratio of these two parameters is in line with that predicted for an invariantplane transformation, indicating that the internal twins come into existence as an integral part of the martensitic transformation. Notwithstanding the constancy of the twin dimensions, the hardness of these martensites increases in the usual way with carbon content. Hence, a solid-solution hardening model is proposed to account for the carbon-dependent strengthening of virgin martensite. A reasonable explanation is obtained through interactions between dislocations and random carbon atoms, assuming a parabolic-hyperbolic potential well and an interaction energy of 0.5 eV. (Author)

Descriptors :   (*MARTENSITE, HARDENING), (*IRON ALLOYS, NICKEL ALLOYS), (*STEEL, MARTENSITE), CARBON ALLOYS, HARDNESS, TRANSFORMATIONS, ELECTRON MICROSCOPY, CRYSTAL DEFECTS, TRANSITION TEMPERATURE, METALLOGRAPHY

Distribution Statement : APPROVED FOR PUBLIC RELEASE