High-throughput investigation of ferrite growth kinetics in graded ternary Fe-C-X alloys

International audienceThe composition dependence of ferrite growth kinetics in Fe-C-X ternary alloyed steels, where X=Ni, Mn, Mo, Cr, Si, was investigated using a high-throughput approach. Compositionally graded samples were subjected to in situ time-and space-resolved X-ray diffraction during intercritical annealing. To this end, diffusion couples were created between a binary Fe-C and different Fe-C-X alloys, using hot uniaxial compression and high temperature diffusion treatments. In-situ high-energy X-ray diffraction experiments were performed to collect ferrite growth kinetics along the composition gradient of the diffusion couples. A large dataset describing the austenite-to-ferrite phase transformation kinetics was generated using a very limited number of experiments. This dataset of unprecedented size was compared to the kinetics predicted by the classical local-equilibrium (LE) and para-equilibrium (PE) models as well as a modified version of the three-jump solute drag (SD) model, which accounts for the different interactions between the elements present at the austenite/ferrite interface. The comparison showed that both LE and PE models fail to capture the effect of both composition and temperature on the kinetics of ferrite growth for the different Fe-C-X systems. The SD model calculations matched experimental transformation kinetics at all investigated temperatures and over almost all the investigated composition ranges of Si, Cr, Mn, Ni, and Mo