title: Carbide characterization in low-temperature tempered steels.
abstract: The nature of the initial carbides formed during the early stages of the tempering of steels is still a matter of debate. Conventionally, the main transition carbide is described as epsilon carbide, with a composition of approximately Fe(2.4)C. However, earlier one-dimensional atom probe (1DAP) results indicated the existence of carbon-rich regions having much lower carbon contents, with maxima of around 10at%. There was some uncertainty about the interpretation of the 1DAP results, because of possible problems with alignment of the aperture and with trajectory aberration effects. We have therefore re-visited this topic, using the three-dimensional (3D) atom probe, and studying both a model Fe-Ni-C alloy and a well-known engineering steel (AISI4340). We demonstrate that, for both materials, low-temperature (20-150 degrees C) aging produces carbon-rich regions with average peak carbon contents of up to 10%. We show for the first time the three-dimensional structure of these carbon-rich regions, and demonstrate that fine-scale faulting exists within them.
authors.affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
authors.forename: Chen
authors.initials: C
authors.lastname: Zhu
authors.forename: Alfred
authors.initials: A
authors.lastname: Cerezo
authors.forename: George D W
authors.initials: GD
authors.lastname: Smith