Three-dimensional analysis of local and dominant habit planes in a lath martensitic stainless steel

The three-dimensional (3D) morphology of lath martensite in a low-carbon 13Cr–4Ni stainless steel (CA6NM alloy) was reconstructed using large-volume Xe+ plasma focused ion beam (PFIB) serial sectioning tomography in combination with electron backscatter diffraction (EBSD). This approach enabled a detailed analysis of both dominant and local habit planes (HPs), offering new insights into their spatial distribution and variation. The dominant HP, determined by averaging the normal directions of high-angle block boundaries (BBs) within packets and across multiple prior austenite grains (PAGs), was found to lie between {111}γ and {557}γ, with an orientation of (0.51,0.52,0.66)γ. However, local HP analysis at individual BBs revealed significant deviations from both orientations in certain regions of the microstructure. 3D morphological observations indicated that bending within specific blocks directly contributed to these local HP variations. It is suggested that interactions between adjacent growing blocks, either through spatial interference and growth competition within a single packet, or hard impingement between blocks from different packets, affect growth paths, ultimately leading to block bending and the macroscopic deflection of interface planes. These findings highlight the intricate interplay between microstructural evolution and crystallographic constraints during martensitic transformation, demonstrating the effectiveness of large-scale 3D characterization in capturing complex microstructural phenomena that are difficult to resolve through conventional 2D analyses.