The effects of elapsed time following gas metal arc welding (GMAW) on the static strength of lap fillet-welded joints were investigated using a static tensile test. It was observed that the static joint strength did not exhibit a time dependency for cases where the fracture was located in each base metal or the softened heat affected zone (HAZ). In addition, the static joint strength was not observed to have a time dependency for cases where a wire with low-hardness weld metal was used and where the fracture was located in the weld metal. However, the static joint strength was low immediately after welding, and increased over time when a wire with high-hardness weld metal was used. It was found that diffusible hydrogen that entered the weld metal during arc welding and was emitted over time was the cause of the time dependency of joint strength. High-hardness weld metal was sensitive to diffusible hydrogen; therefore, time dependency was observed only when wires with high-hardness weld metal were used and the fracture positions were located in the weld metal during tensile tests. In addition, a correlation between the storage temperature following welding and the static strength or diffusible hydrogen content of welded parts was found: the higher the storage temperature, the earlier the joint strength increases, and the earlier the diffusible hydrogen decreases.

This study tries to reveal the mechanism of forming fine and dense oxide particles in oxide dispersion strengthened (ODS) ferritic steel during heat treatment after mechanical alloying (MA). The MAed powders with and without titanium are set to the heat treatment from 873 K to 1423 K and analyzed by small angle X-ray scattering and X-ray diffraction using synchrotron radiation, transmission electron microscopy, and 3D atom probe. Yttrium and oxygen are segregated along the grain-boundaries induced by MA and form clusters after 873 K annealing. Fine oxide particles are densely formed before primary-recrystallization of the nano-sized grains induced during MA, at 973 K. The formation of cubic-Y₂O₃ and Y₂Ti₂O₇ are observed at 1273 K and above, where the size reduction of the oxide particles by Ti-addition is clearly shown.

The corrosion potential and corrosion rate of steel under wet/dry transitions were investigated using the Kelvin probe/pressure difference measurement system in order to elucidate the effect of Sn on the corrosion of steel covered by a thin electrolyte film in wet/dry environments containing chloride ions (Cl⁻). The corrosion rate in the case of an electrolyte containing Cl⁻ during the drying stage was higher than that in the case of an electrolyte containing sulfate ions (SO₄²⁻). Cl⁻ accelerate the hydrolysis of Fe³⁺ and lead to the acidification of the anode site in the thin electrolyte film, while also contributing to corrosion during the drying stage. The Sn-bearing steel showed a lower corrosion rate during the drying stage than that of the mild steel. This was because the Sn ions from the steel can exist stably in the acidic thin electrolyte film and inhibit the anodic reaction during the drying stage. Thus, the superior corrosion resistance of the Sn-bearing steel under atmospheric conditions is attributable to the retardation of the anodic reaction during drying by Sn ions.

In the case of metals, it is considered that the crystal grain refinement due to plastic deformation is caused by the operation of various slip systems in a grain. In order to understand the initial stage of the grain subdivision, a simple shear test was performed on a low-carbon-steel polycrystal having an average grain size of approximately 150 μm.

After the application of 10% shear, several regions having different slip lines were observed in a grain. The slip lines were explained by {110}<111> slip-system of body-centered cubic iron, and the operated Burgers vectors were estimated. The crystal orientations were different for the subdivided regions, and misorientation angles of the crystal rotation were approximately 10°. The rotation axes of the crystal rotation across the subdivided regions were determined. The rotation axes were almost perpendicular to either of the estimated Burgers vectors in the subdivided regions. The directions of the rotation axes are discussed.

Phase equilibria among the refractory bcc solid solution (bcc_ss), B2, and Laves phases in Nb-Cr-NiAl and Nb-V-NiAl isothermal sections were studied with the aim of introducing the NiAl-B2 phase and/or Al-containing Laves phase for improvement of the oxidation resistance of the bcc_ss phase as an Al reservoir layer for the Al₂O₃ surface layer. Laves phases appear in a wide composition range in both of the isothermal sections, which prevent equilibration of NiAl-B2 with the Nb-rich bcc_ss phase. The geometrical model proposed by Edwards was applied to understand the site-substitution behavior of the multi-component AB₂ Laves phase. In the Nb-Cr-NiAl, Nb-V-NiAl, and Nb-Mo-NiAl systems, the site-substitution behavior of the Laves phases could be explained by comparison of the average atomic diameters of NiAl-B2, Cr, V, and Mo.