Effects of dislocation planarity and compositional complexity on hydrogen embrittlement of austenitic steels
Stable austenitic steels have been recognized as hydrogen-resistant materials. However they also show hydrogen-assisted failure when exposed to a severe hydrogen atmosphere, e.g. 100-MPa hydrogen gas. In this talk, we present two examples of hydrogen embrittlement of stable austenitic steels: Fe25Cr1N steel and equiatomic high-entropy alloy. The former shows extremely enhanced dislocation planarity because of the Cr-N coupling. The strong dislocation planar motion causes stress concentration on grain boundaries, which results in intergranular fracture when hydrogen is introduced. In addition, the dislocation planar array can act as quasi-cleavage fracture path. Therefore, the hydrogen-assisted failure in the high-nitrogen steel occurs via dislocation-planarity-driven microstructural cracking. The high-entropy alloy shows hydrogen-assisted intergranular fracture. The brittleness can be reduced by grain refinement or reducing Mn content. In the presentation, details of these phenomena are given with electron channeling contrast images.
Prof. Dr. Motomichi Koyama
Environmentally Robust Materials
Akiyama Laboratory
Tohoku University
2 Chrome-1-1 Katahira, Aoba Ward, Sendai, Miyagi 980-8577
Japan
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