The solidification microstructure of Ni-hard type cast iron was investigated to evaluate the influence of Mo and W additions on the formation of carbides and graphite. The specimen was prepared based on the composition of Fe-3.3%C-0.8%Si-0.8%Mn-4.4%Ni in mass%, and Mo or W was added to the reference specimen to a maximum of 6.7%Mo or 2.9%W, respectively. Each alloy was cast into a permanent mold for the microstructural analysis. The solidification process of each alloy was also investigated by thermal analysis and quenching experiments. According to EDS and XRD analyses, it is revealed that the solidification microstructure of standard Ni-hard type cast iron consists of primary γ, γ+M₃C eutectic structure and graphite, and the addition of Mo and W provides γ+M₂C eutectic structure. The further addition of Mo and W increases the amount of γ+M₂C eutectic structure and decreases the amount of γ+M₃C eutectic structure, whereas it has little effect on the amount of primary γ. The quenching experiment reveals the graphite formation as eutectic structure between the formations of γ+M₂C eutectic structure and γ+M₃C eutectic structures. The addition of Mo reduces the amount of graphite, while addiction of W increases the amount of graphite. The influence of each alloying element on graphite formation could be estimated by carbon solubility and the composition of the residual liquid.

In this study, we obtained elemental distributions around the scratch in reinforced concrete. Confocal micro-X-ray fluorescence (CM-XRF) technique was employed for observing a sample cross section without destroying the sample. We prepared a rebar fragment, and then it was covered with concrete. The test sample was scratched with the band saw with a blade of ~1 mm width. The scratched test sample was measured using a laboratory-made CM-XRF instrument. As for the Ca distribution, the thickness of the concrete layer was estimated to be ca. 100 μm. In addition, the depth and width of a scratch were calculated to be ca. 150 μm and 1.1 mm, respectively, as observed from the Fe distribution. And then, we observed the corrosion products resulted by immersing the reinforced concrete in NaCl solution. Sphere-shaped structures were seen in the Fe and Cl distributions, therefore, we considered that it to be the corrosion product containing iron chloride. It is expected that by using a sample cell for in-situ observation, it will be possible to observe the corrosion process of reinforced concrete in real time.

To improve the prediction accuracy of oil quenching distortion, the transformation plasticity coefficient was determined by oil quenching experiment on the steel sheet and numerical simulations. The cooling curve of the steel sheet during oil quenching and the deflection after quenching were measured under three experimental conditions. In the first condition, austenitic stainless steel sheet was quenched into cold quenching oil for confirmation of the validation of the temperature prediction results by the numerical simulation. In the second condition, chromium molybdenum steel sheet was quenched into cold quenching oil for confirmation of the validation of the latent heat predicted by the numerical simulation. By fitting the results of the numerical simulation to the deflection of the sheet in this experiment, the transformation plasticity coefficient in the martensitic transformation of the chromium molybdenum steel was determined to be 21×10⁻⁵ MPa⁻¹. In the third condition, chromium molybdenum steel sheet was quenched into semi-hot quenching oil to verify the accuracy of the prediction of heat treatment distortion using the determined transformation plasticity coefficient. The error in the deflection of the sheet after oil quenching using the determined transformation plasticity coefficient was reduced to 6% from 64% (the previous report). The accuracy of distortion prediction was improved by changing the specimen morphology used in oil quenching experiments from bars to sheets.

During hot stamping, Zn oxidation occurs on the surfaces of Zn-coated steel sheets such as galvanized iron and galvannealed sheets. In order to elucidate the effect of Al in the Zn coating layer on the Zn oxidation, the present study investigated the amount of ZnO formed on the Zn-coated steel sheets with and without Al addition to the coating layer. The amount of ZnO was found to decrease upon Al addition. The microstructural analysis of the Zn-coated steel sheets with Al addition revealed that the added Al became the ZnAl₂O₄ layer at the interface between the ZnO layer and Zn coating layer after hot stamping. As a result, Zn oxidation is considered to be suppressed by the presence of the ZnAl₂O₄ layer.

The purpose of this report is to compare the coating structure and corrosion mechanism of newly developed Zn-19%Al-6Mg-Si with conventional Zn-Al-Mg alloy coating Zn-11%Al-3%Mg-0.2%Si. In past papers the corrosion resistance of Zn-Al-Mg alloy coating layers was mainly discussed based on analysis methods that focus on one aspect of early corrosion stage. However, this report focuses on the changes in the corrosion mechanism until the end of the coating lifespan and picks up the factors of the coating layer that contribute to corrosion resistance.

The results of the corrosion cross section images of the Zn-Al-Mg alloy coating layer after cyclic corrosion test suggested that corrosion of the coating layer progresses selectively in each phase, which means each phase has its own electrochemical potential. Considering the differences in the corrosion mechanisms of these two coated steel sheets, it was suggested that the phase proportion of the coating layer and the unique potential determine the corrosion resistance of the coating layer.

Vanadium composite electrogalvanized (Zn-V hydroxide) steel sheets were prepared by electroplating using a horizontal flow cell. The structure of Zn-V plating layer depended on the flow rate of electrolyte and the current density, and the performance of Zn-V steel sheets depended on the structure of plating films. The Zn-V plating films composed of two-phase structure without cracks showed the high corrosion resistance and high adhesion. The two-phase layer consisted of the field oriented fiber and non-field oriented texture. The field oriented fiber phase was mainly composed of metallic Zn, and the non-field oriented phase was mainly formed from the amorphous V compound. The V compound in the non-field oriented phase seems to be formed by the hydrolysis reaction of V ions due to pH increase in cathode layer according to hydrogen evolution during Zn-V plating. The Zn-V steel sheets had a black and low-gloss appearance compared to the conventional electrogalvanized steel sheet (EG). Since the V compound in the non-field oriented texture was black and the field oriented texture formed the surface roughness, the lightness and gloss of the Zn-V steel sheets decreased with increasing V content in plating films.

Crack initiation and propagation behavior in hydrogen embrittlement fracture of tempered martensitic steel at a low hydrogen content was compared with the results at a high hydrogen content. Notched specimens charged with a low hydrogen content of 0.18 ppm and a high hydrogen content of 5.3 ppm were stressed and unloaded immediately upon reaching the maximum stress in tensile tests. At the low hydrogen content, quasi-cleavage (QC) fracture was dominant at the notch tip, and mixed intergranular (IG) and QC fractures were observed away from the notch tip. A crack initiated in the prior γ grains at the notch tip and propagated along the {011} plane. The crack initiation site corresponded to the site of maximum equivalent plastic strain. The other crack initiating on the prior γ grain boundaries was observed at a site away from the notch tip. Microvoids were formed discontinuously inclined at about 45° to the tensile axis direction between these two types of cracks observed at the low hydrogen content. In contrast, at the high hydrogen content, cracks initiated on the prior γ grain boundaries away from the notch tip. The crack initiation site corresponded to the vicinity of the region where both the principal stress and hydrogen concentration were high. These findings indicate that crack initiation at the low hydrogen content is not necessarily consistent with the site of the maximum principal stress and the local hydrogen concentration, unlike the case of the high hydrogen content.