Showing papers by "Masaaki Nakai published in 2005"
TL;DR: In this article, the system free energy of the martensite phase of an Fe-Cr-C ternary alloy was estimated, where Gsys =G0+Esurf+Estr+Esurf, where Esurf is the chemical free energy, G0 is the interfacial energy for the boundaries of the microstructure, and Estr is the elastic strain energy due to the dislocations.
Abstract: The system free energy was estimated for the martensite phase of an Fe-Cr-C ternary alloy. The system free energy of the martensite phase is defined as, Gsys=G0+Estr+Esurf, where G0 is the chemical free energy, Esurf is the interfacial energy for the boundaries in the martensite microstructure, and Estr is the elastic strain energy due to the dislocations in the martensite phase. From the experimental results on SEM/EBSD, the interfacial energy was estimated to be 0.05 J/mol for the prior austenite boundary, 0.11 J/mol for the martensite packet boundary and 0.32 J/mol for both the martensite block and the lath boundaries in the asquenched specimen. The total decrement in the interfacial energy accompanying annealing at 873 K for 100 h after quenching was estimated to be about 0.1 J/mol. Also, the elastic strain energy of the asquenched specimen was estimated to be 7.1 J/mol. The total microstructural energy of the martensite phase was about 10 J/mol, which operates as a driving force for the microstructure evolution, e.g., recovery of dislocations and the coarsening of the sub-structures such as martensite-packet, -block and -lath.
46 citations
TL;DR: In this article, the authors investigated the hydrogen dissolution in the oxide scale during the steam oxidation of pure iron and ternary ferritic steel, and they found that the amount of dissolved hydrogen was much larger in the ferric steel than in pure iron.
Abstract: The high-temperature oxidation in both air and steam was examined experimentally with pure iron and a Fe-10Cr-0.08C (mass%) ternary ferritic steel. 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 ternary ferritic steel, the oxide scale formed was much thicker in steam than in air. Thus, the oxidation rate was nearly independent of the air and the steam atmosphere for pure iron, but was dependent for the ternary ferritic steel. In the present study, this difference was investigated from a viewpoint of the hydrogen dissolution in the oxide scale during the steam oxidation. The amount of dissolved hydrogen was measured using a thermal desorption spectroscopy (TDS). It was found that the amount of the dissolved hydrogen was much larger in the ternary ferritic steel than in pure iron. Also, it was shown that the hydrogen dissolution in the ternary ferritic steel was related to the presence of (Fe,Cr)3O4 in the oxide scale. The defect structure in this chromium-rich oxide was modified by hydrogen dissolution, so that the ionic diffusion could be enhanced in it, resulting in the more accelerated oxidation rate in steam.
29 citations
TL;DR: In this article, the amount of hydrogen dissolved into Fe-10Cr-0.08C-0∼0.035 (mass%) steels during the steam oxidation at 923 K was measured by thermal desorption spectroscopy (TDS).
Abstract: The amount of hydrogen dissolved into Fe-10Cr-0.08C-0∼0.035 (mass%) steels during the steam oxidation at 923 K was measured by thermal desorption spectroscopy (TDS). The amount of dissolved hydrogen was found to be dependent largely on the steam oxidation resistance of the steels. In other words, it was much smaller in the sulfur-doped steels with good oxidation resistance than in the sulfur-free steels with poor oxidation resistance. Thus, we suggest that the hydrogen dissolution is one of the most important factors to understand the steam oxidation resistance of the steels.
13 citations