A common, serviceable form of steel has been observed by employing synchrotron X-ray microtomography technique. Spatial resolution has been optimized using a test object with varying experimental conditions. Reasonably high resolution, which is close to the theoretical upper limit for the projection-type Xray tomography, has been achieved for a reasonably large specimen. Its application has made it possible to clearly observe a fatigue crack and its opening behavior in steel, and to demonstrate some quantitative mechanical evaluations.

Spatial resolution of 3D images obtained by synchrotron X-ray microtomography technique is evaluated using cyclic bar patterns machined on a steel wire. Influences of X-ray energy and the sample-to-detector distance on spatial resolution were investigated. Relatively high X-ray energies of 33-78 keV are applied due to the low X-ray transmission of transition metals. Best spatial resolution of about 1.2 µm was observed at the sample-to-detector distance range of 20-110 mm and at the energy range of 68-78 keV. Several factors such as X-ray scattering and diffraction phenomena affecting the degradation of spatial resolution are also discussed.

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