Fe-Cr 系合金の耐高温水蒸気酸化性と水素侵入
High-temperature oxidation of a pure iron, Fe-2Cr alloy, Fe-10Cr alloys and an Fe-10Cr-0.08C steel was examined in both air and steam at 923 K. In case of pure iron, the thickness of the oxide scale formed in steam at 923 K for 360 ks was comparable to that of the scale formed in air. On the other hand, in case of the Fe-Cr binary alloys and the ternary martensitic steel, the oxide scale was much thicker in steam than in air. The amount of hydrogen dissolved into the pure iron and the steels during exposure to the high-temperature steam was measured with thermal desorption spectroscopy (TDS). It was found that the amount of the dissolved hydrogen in the oxide scale was much larger in both the binary alloys and the ternary ferritic steel than in pure iron, and then it leads to the more accelerated oxidation rate of the binary alloys and the ternary steel in the steam. Furthermore, the martensite structure of the ternary steel exhibited an excellent oxidation resistance in air compared to the ferrite phase in the same steel. This is probably because the martensite phase has a lot of plane defects such as block boundaries for the fast diffusion path of Cr element.