On the correlation between the habit plane and 3D morphology of lath martensite: A direct 3D observation using serial sectioning tomography of a low-carbon stainless steel

The crystallography and morphology of lath martensite in a low-carbon 13Cr-4Ni stainless steel were analyzed by large-volume, high-resolution serial sectioning tomography using a combination of Xe plasma focused ion beam (PFIB) and electron backscatter diffraction (EBSD) analysis. The extracted 3D EBSD results were compared with 2D observations, and potential misinterpretations arising from 2D analyses were highlighted. 3D reconstruction of the packets revealed that the volume of each prior austenite grain (PAG) is occupied with four distinct types of packets, arranged as a specific tetrahedral pattern in 3D. Through geometrical calculations, a direct link between 3D characteristics of this tetrahedral pattern and the dominant habit plane of the microstructure, {557}γ, was established. These findings, unattainable through 2D characterizations, are expected to enhance our understanding of lath martensite formation and inform recent modeling efforts aimed at accurately representing the 3D structure and mechanical properties of these alloys.