In-situ Grain-Resolved Austenite–Ferrite Transformation in Hypoeutectoid Rail Steel

This experiment aims to directly observe the disappearance of a single austenite grain in hypoeutectoid rail steel during controlled cooling using dark-field X-ray microscopy (DFXM) at 17 keV. A partially transformed austenite grain will first be stabilized at high temperature and tracked isothermally to quantify early growth and intragranular strain. Subsequent stepwise cooling will capture the nucleation of proeutectoid ferrite at specific boundary segments, followed by the eutectoid transformation of the remaining carbon-enriched austenite. Real-time energy rocking and mosaic scans will provide 3D strain and orientation maps of both phases during the transformation. The results will reveal how transformation strain is accommodated, how boundary ferrite influences subsequent pearlite formation, and whether early and late ferrite store different residual strain signatures, providing a benchmark dataset for phase-field and transformation models in rail steels.