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A new observation method was developed for visualizing subgrains on the
chemical-mechanically polished surface of ferritic heat-resisting steels, using field
emission-type (FE) SEM. The backscattered electron images revealed clearly
visualized subgrain structures that were not influenced by the presence of
precipitated particles.
The authors then investigated the use of FE-backscattered electron images to
visualize low-angle boundaries such as subgrain boundaries. The specimen
surface must be free of any strain or unevenness, so in this study the authors
adopted the new technique of chemical mechanical polishing, which involves the
simultaneous application of chemical corrosion and mechanical polishing to
prepare specimen surfaces for structural observation.
In this study, subgrains of ferritic heat-resisting steels were quantified based on
the microstructural observation. In particular, we focused on differences in the
distributions of subgrains for two types of 12Cr-2W steels with different creepfatigue
susceptibility and investigate the relationships between creep-fatigue
properties and changes in subgrains.