Rc. Reed et al., DETERMINATION OF REAUSTENITIZATION KINETICS IN A FE-0.4C STEEL USING DILATOMETRY AND NEUTRON-DIFFRACTION, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 256(1-2), 1998, pp. 152-165
The contraction associated with austenite formation in a high purity a
lloy of nominal composition Fe-0.4C (wt%) has been determined using a
non-contact laser dilatometer. Both isothermal and continuous heating
experiments have been carried out. Interpretation of the results requi
res accurate estimates of the lattice parameters of the phases at the
reaction temperatures; these have been measured using neutron diffract
ion, with the lattice parameters of cementite being measured on a furt
her steel of composition Fe-2.77C (wt%). Using a rule of mixtures, it
is shown that the dilatometrical results cannot be rationalised unless
the dissolution of cementite is accounted for. The experimental data
have been compared with predictions from a theoretical model which ass
umes that the growth of austenite is diffusion-controlled and associat
ed with the dissolution of cementite, in two distinct ways. First, exp
erimental and theoretical time-temperature-transformation (TTT) diagra
ms are computed, the experimental curves being deduced from the dilato
metrical data. Second, the contraction associated with reaustenitisati
on during continuous heating is modelled and compared with experiment.
This has involved modifying the theoretical model to account for anis
othermal transformation, and the details are presented. Despite the fa
ct that the model assumes a very simplified geometry, it is shown that
theory and experiment are in broad agreement, with the model able to
explain the major characteristics of the transformation. (C) 1998 Else
vier Science S.A. All rights reserved.