Efficient 3D observation of steel microstructure using serial sectioning with precision cutting and on-site etching

This paper describes a fast and precise 3D observation method for steel microstructures using a cutting-based serial sectioning system with on-site etching. The method employs automated 3D internal structure microscopy for ferrous materials and on-site manual etching without detaching the specimen during the process. A notable feature of this system is that it uses precision cutting instead of polishing for surface fabrication, which has advantages in the fabrication speed, applicability in dry conditions, and controllability of the fabrication depth. The precision cutting of a dual-phase (DP) steel achieved a low roughness comparable to polishing. Furthermore, the on-site etching process by dropping etchant yielded sufficient contrast between ferrite and martensite phases. Observation of DP steel cross sections at 1 μm intervals afforded a 3D image in the range of 690 × 518 × 103 μm3 with a resolution of 0.144 × 0.144 × 1.0 μm3. The processing time was approximately five minutes for each cross section and almost half a day for the whole image, which was much more efficient than manual serial sectioning that requires a few weeks. The microstructures were also visible in reconstructed lateral cross sections of the 3D image, which proved the sufficient quality of our imaging. In addition, the segmented volume revealed the non-uniform martensite distribution among cross sections quantitatively. Most of them were connected in 3D, while they seemed to be separated in 2D. These results demonstrated the usefulness of our method with precision cutting and on-site etching.