The X-ray microbeam diffraction technique is a powerful method for observation of substructures in metallic materials, because of its ability to measure the microstructural changes in a localized region quantitatively and non-destructively. In recent years, the microstructure in the vicinity of fatigue crack tip has been investigated by using this technique and the mechanism of crack propagation has been discussed based on the results obtained. However, the correlation of the X-ray microbeam

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... fraction patterns and the microstructures observed by the other methods has not been made sufficiently clear. In the present study, the X-ray microbeam diffraction patterns from deformed specimens were compared with the substructures photographed by means of transmission electron microscopy. The material used was 0.12% carbon steel, and the low cycle fatigue test, the high cycle fatigue test and the impact test were performed to form substructures in the specimens. A good correlation was obtained qualitatively between the X-ray microbeam patterns and substructures in both the low cycle fatigued and impacted specimens. It was possible to distinguish the mode of substructure through X-ray microbeam diffraction patterns. A disagreement existed, however, between the values of subgrain size obtained by different analytical methods. It is considered that getting agreement between these values is difficult in the present stage, because of the assumptions on analyses. But the subgrain size should be a good parameter representing the plastic deformation, if an analytical method suitable for the mode of diffraction pattern is adopted.