Experimental Investigation of Bainite Microstructure in Fe-C

In this work, we present an experimental investigation of the bainite microstructure in pure Fe–C systems. Although Fe–C alloys are of fundamental importance to steel, the microstructure of metastable undercooled austenite—particularly the mechanism of bainite formation—remains a subject of debate. This uncertainty arises from the limited number of experimental studies available for the Fe–C system and the controversial interpretations of existing results. To address this gap, we employed a comprehensive set of methodologies, including heat treatment with dilatometry, light microscopy, scanning electron microscopy (SEM) with in-situ nanoindentation, and transmission electron microscopy (TEM), to characterize bainite and related metastable microstructures (such as pearlite, acicular ferrite, Widmanstätten ferrite, and martensite). Our results reveal that bainite formation competes with other metastable microstructures, complicating both its development and conventional characterization. By integrating these complementary techniques, we achieve a more complete and reliable characterization of bainite in the Fe–C system.