Carbide characterization in low-temperature tempered steels.

Journal article

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: Zhu, C; Cerezo, A; Smith, G

• Publication status: Published
• Journal: Ultramicroscopy
• Volume: 109
• Issue: 5
• Pages: 545-552
• Publication date: 2009-04-01
• DOI: 10.1016/j.ultramic.2008.12.007
• EISSN: 1879-2723
• ISSN: 0304-3991
• Language: English
• Keywords: Carbon segregation; 4340; LEAP; Fe-Ni-C; Low-temperature tempering; 3DAP