微小疲労き裂近傍の組織観察例と耐疲労鋼創製の指針

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  • Alloy design strategy for fatigue-resistant steels and associated microstructure observations at a small fatigue crack tip

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<p>I here present recent examples of crack tip microstructure observations. In particular, special emphasis is placed on dislocation microstructure evolution near a small fatigue crack tip, observed by electron backscatter diffraction measurements and electron channeling contrast imaging. Both of the techniques can show microstructures at a specific location such as plastic zone at a crack tip in a bulk specimen. The first example is a case of metastable austenitic steels which initial microstructures transform to body-centered cubic or hexagonal close-packed phase. The second and third examples are given in Fe-Mn-C and Fe-Cr-N stable austenitic steels. With these examples, effects of transformation, strain aging, and dislocation planarity on small crack growth resistance are revisited. Moreover, I present successful examples of in situ electron channeling contrast imaging of dislocation motion at a small fatigue crack tip in the Fe-Cr-N austenitic steel. The in situ characterization results implied significant contribution of dislocation stress shielding and planar slip-induced damage evolution on resistance to Mode I and II small fatigue crack growth.</p>

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