Decomposition of martensite during tempering of rhenium steels

Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality

“…The tetragonality is partially recovered during heating to room temperature, although never reaches its expected value described by the relation c/a  1  0.046с С , where c C is the carbon concentration in mass %. The abnormally low tetragonality was found after low-temperature martensitic transformation in Fe-Mn-C [12], Fe-Ni-C at a moderate Ni content of 8% [13], Fe-Re-C [14] and plain high carbon [15] martensites. Two main hypotheses have been proposed to interpret the abnormally low tetragonality of the virgin iron-carbon martensite: (i) a partial location of carbon atoms in the tetrahedral interstitial sites resulted from the    martensitic transformation through the intermediate -phase [16]; (ii) a redistribution of carbon atoms among three sublattices of octahedral sites in the bcc crystal lattice due to a twinning on the (011) planes in the course of the low-temperature martensitic transformation [17].…”