An Atom Probe Study of Κ-Carbide Precipitation in Austenitic Lightweight Steel and the Effect of Phosphorus


The influence of phosphorus on κ-carbide precipitation and alloy partitioning in an austenitic Fe-30Mn-9Al-1Si-0.9C-0.5Mo cast steel was studied utilizing a combination of transmission electron microscopy, 3D atom probe tomography, X-ray diffraction, and first-principles atomistic modeling. Increasing the amount of phosphorus from 0.006 to 0.043 wt pct P increased the kinetics of the initial ordering reaction. Specimens from the high-phosphorus steel showed some degree of short-range ordering of Fe-Al-C that took place during the quench. It was shown that phosphorus increases both the size and volume fraction of κ-carbide during aging. However, the distribution of phosphorus appears to be homogeneous, and thus long-range diffusion of phosphorus was not responsible for the observed increase in hardening. It is shown that phosphorus encourages the initial short-range ordering into the E21 structure of κ-carbide and also accelerates spinodal decomposition associated with carbon and aluminum diffusions.


Materials Science and Engineering

Second Department



This study was supported in part by the Army Research Laboratory under contracts from Battelle Memorial Institute (contract W911NF-07-D-0001) and Benet Laboratories (contract W15QKN-07-2-0004), and by the National Science Foundation€™s MRSEC program (DMR-0520513) and made use of its Shared Facilities at the Materials Research Center of Northwestern University. Laura Bartlett was also supported by a U.S. Department of Education GAANN fellowship under contract P200A0900048. The FEI Tecnai F20 scanning/transmission electron microscope was obtained through a Major Research Instrumentation grant from the NSF under contract DMR-0922851.

Keywords and Phrases

Alloy steel; Aluminum; Austenite; Carbides; Carbon; High resolution transmission electron microscopy; Manganese; Molybdenum; Precipitation (chemical); Probes; Reaction kinetics; Spinodal decomposition; Transmission electron microscopy; X ray diffraction, 3d atom probe tomographies; Atomistic modeling; Carbide precipitation; First principles; Light-weight steels; Long-range diffusion; Order reactions; Short range ordering, Phosphorus

International Standard Serial Number (ISSN)

1073-5623; 1543-1940

Document Type

Article - Journal

Document Version


File Type





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Publication Date

01 Nov 2017