Abstract
Transmission electron microscopy (TEM) observations of 1.95 wt pct C martensite samples, aged at 330 and 352 K for 1 and 2 hours, respectively, confirm the fact that the two steps of aging, as evidenced by Mössbauer spectroscopy kinetics study, are due to clustering and subsequent long-range ordering. Streaks are observed along 〈203〉* directions during clustering, and in addition, two types of split superstructure spots appear during ordering at the advanced stage of aging. These are tentatively explained by a 1C-2Fe-1C-5Fe-1C-5Fe sequence of carbon and iron atoms arranged along [001]α′, which gives rise to antiphase domains with a 12a superperiod within the alternating carbon-rich and carbon-depleted regions, wherea is the lattice parameter of body-centered cubic (bcc) iron. The associated formula is Fe6C. In the first stage of tempering, the orthorhombic structure of the precipitated carbide is confirmed, while evidence of ordering as in Co2N is lacking. The Fe9C4 stoichiometry, which is close to the experimental Fe2.4C, is instead proposed forε- orη-carbide.
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Former Graduate Student of the University of Nancy and Laboratoire CNRS Maurice Letort
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Uwakweh, O.N.C., Génin, J.M.R. & Silvain, J.F. Electron microscopy study of the aging and first stage of tempering of high-carbon Fe-C martensite. Metall Trans A 22, 797–806 (1991). https://doi.org/10.1007/BF02658989
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DOI: https://doi.org/10.1007/BF02658989