Resolving solidification-derived heterogeneities in a martensitic stainless steel by large-volume PFIB tomography

Large-volume PFIB-based 3D-EBSD/SEM tomography was used to resolve solidification-derived heterogeneities in a CA6NM martensitic steel. δ-ferrite particles, inclusions, and micropores were reconstructed in 3D, revealing distinct morphologies and spatial distributions. δ-ferrite morphology depends on proximity to prior-austenite grain boundaries, with boundary-attached particles remaining elongated and faceted, whereas particles within grain interiors evolve into small, spheroidal remnants. Micropores were classified into gas, gas-shrinkage, and shrinkage pores, while inclusions were uniformly small and near-spherical. Spatial analysis shows strong clustering of micropores relative to the more uniform distribution of δ-ferrite, highlighting the capability of PFIB-based 3D characterization to quantify solidification-derived heterogeneities in martensitic steels. • Large-volume PFIB tomography enables 3D analysis of casting heterogeneities. • δ-ferrite morphology varies from faceted boundary particles to spheroidal interiors. • 3D morphology distinguishes gas, gas-shrinkage, and shrinkage pores. • Spatial statistics reveal distinct clustering behaviors of defects.