Optimization of preparation methods for EBSD analysis of highly metastable austenitic steels

The preparation process of highly metastable austenitic steels can cause a mechanically induced martensitic phase transformation, significantly affecting the quality and validity of subsequent microstructural examinations. In the as-built (untreated) state, specimens additively manufactured from the corrosion-resistant, martensitic knife steel 1.4116 (X50CrMoV15-1, DIN EN 10088) by powder bed fusion-laser beam/metal exhibit the peculiarity of an almost fully austenitic microstructure. This microstructure is, however, thermodynamically metastable, thus forming undesirable deformation martensite during the metallographic preparation for electron backscatter diffraction (EBSD) investigations. This article therefore discusses the application and optimization of metallographic preparation methods with a focus on minimizing preparation-related artifacts. The core question in this work is whether varying the preparation methods and parameters leads to a reduction in the formation of deformation martensite. The α’ content was measured in between the preparation steps using a Ferritscope ® to investigate the impact of the preparation on the microstructure. The resulting microstructures were analyzed using EBSD and compared to assess the preparation method’s impact on the quality of the EBSD data. The investigations showed that the grinding/polishing pressure and relatively small differences in the alloy composition considerably affect the preparation result.