In Situ Investigation of the Iron Carbide Precipitation Process in a Fe-C-Mn-Si Q&P Steel

Quenching and Partitioning (Q&P) steels are promising candidates for automotiveapplications because of their lightweight potential. Their properties depend on carbon enrichmentin austenite which, in turn, is strongly influenced by carbide precipitation in martensite duringquenching and partitioning treatment. In this paper, by coupling in situ High Energy X-RayDiffraction (HEXRD) experiments and Transmission Electron Microscopy (TEM), we give someclarification regarding the precipitation process of iron carbides in martensite throughout the Q&Pprocess. For the first time, precipitation kinetics was followed in real time. It was shown thatprecipitation starts during the reheating sequence for the steel studied. Surprisingly, the precipitatedfraction remains stable all along the partitioning step at 400 ◦ C. Furthermore, the analyses enable theconclusion that the iron carbides are most probably eta carbides. The presence of cementite was ruledout, while the presence of several epsilon carbides cannot be strictly excluded