Composition of cementite in the dependence on the temperature. In situ neutron diffraction study and Ab initio calculations

C-vacancy concentration in cementite, Fe3C1−, in equilibrium with α-Fe[C] and γ-Fe[C]

“…Similar first-principles calculations by Jiang et al [28] have led to a value of E Va = 0.63 eV, which, however, was not obtained on the basis of energies from EOS fitting. The latter was also not the case for Voronin et al [17], who obtained E Va = 0.2 eV. Thereby, paramagnetism of the cementite was modeled by adopting an antiferromagnetic ordering of the Fe atoms.…”

“…Data suitable for comparison with the presently determined values of K [17] are not sufficiently resolved to quantify lattice parameter changes with composition change.…”

“…Much smaller C contents in cementite, even at T 6 900 K (i.e. below the eutectoid temperature) were reported [17]: Rietveld refinements performed on neutron powder-diffraction patterns collected from dual-phase a + h Fe-C alloys gave C contents in cementite decreasing with increasing temperature. C contents corresponding to a formula of Fe 3 C 0.75 were encountered close to the eutectoid temperature.…”

Understanding the Behavior of Advanced High-Strength Steels Using Atom Probe Tomography

“…pct carbon content in Fe 3 C. This could be explained, as mentioned previously, by carbon vacancy formation in cementite. [50] Evolution of cluster/fine precipitate composition as a function of size for both studied conditions is shown in Figure 11. As seen from Figure 11, the C content in clusters has a similar dependence on cluster size when the sizes are smaller than 3 nm in both conditions.…”

“…[21] However, as has been recently shown by neutron diffraction studies and ab initio calculations, the composition of cementite continuously varies with temperature having Fe 3 C x composition due to low energy for carbon vacancies formation. [50] The presence of various nonstoichiometric iron carbides and their transition was also predicted using first-principles calculations, and was associated with the possible stabilization by coherency strains with the surrounding iron-rich matrix. [51] Due to the difference in the processing schedule and the higher Mo content, a larger variety of carbides was present in steel 2 compared with steel 1.…”