Since it has been urgently demanded to secure the secondary phosphorus resources domestically in addition to the establishment of a stable supplying path of phosphate ore from overseas, the recovery of phosphorus from steelmaking slags is attracting attention. The phosphorus-enriched slag obtained by dephosphorizing the high phosphorus hot metal, which was prepared by the reduction of conventional steelmaking slag, is thought to be useful as a raw phosphorus resource. It was reported in our previous paper that phosphorus can be effectively separated from P-enriched slag by the citric acid leaching method. In this study, the effects of citric acid concentration in solution, solution temperature, slag/solution mass ratio, and P-enriched slag composition on phosphorus dissolution behavior were additively investigated. A phosphorus dissolution from the P-enriched slag was significantly promoted by increasing the citric acid concentration in solution. However, even if the solution temperature was increased during leaching, the speed and ratio of phosphorus dissolution from the P-enriched slag did not change. With increasing the slag/solution mass ratio, the concentration of each element in solution increased, while their dissolution ratios decreased. Furthermore, the phosphorus dissolution ratio was suppressed in the case of the P-enriched slag with low CaO and high P₂O₅ concentrations. Appropriate conditions for various factors affecting phosphorus dissolution behavior from P-enriched slag were discussed.

Dissimilar welding of thin plates of conventional pure titanium and steel was investigated using an insert metal of the chromium plate to avoid the formation of brittle intermetallic compounds consisting of Ti and Fe. The Cr atom also can form intermetallic compounds with Ti atom though the formability is less than that of Ti/Fe. Therefore, the effect of dilution of Cr on the forming of intermetallic compounds in the weld metal by laser welding process, which has larger cooling rate comparing to the conventional arc welding, was evaluated. The weld metals with various level of dilution by Cr were obtained by adjusting the offset of laser beam irradiation from the interface of titanium and chromium plates. As the result it was found that the formation of intermetallic compound was prevented in the condition of the dilution lower than about 40%. However, the excess offset to reduce the dilution of chromium plate can cause weld defects such as the lack of fusion. That problem was solved by achieving low dilution with the addition of titanium wire in the laser welding process without offset. In conclusion, it was confirmed the sound dissimilar welded joints resulting in sufficient mechanical properties were obtained by applying the proper welding condition based on the findings in this work.

Electrodeposition of Zn–Zr compound composite was performed under pulsed and double pulsed current conditions at 313 K on unagitated pH 2 sulfate solutions containing Zn²⁺, ZrO²⁺ ions and a polyethylene glycol (PEG). At constant current density of 5000 A∙m⁻², the coarse granular deposits containing Zr compound existed partially. Meanwhile, in pulse electrolysis, the coarse deposits were rarely seen and the both areas of deposited films containing Zr compound and its films being exfoliated were observed. On the contrary, in double pulse electrolysis of high current density (5000 A∙m⁻²) and low current density (500 A∙m⁻²), the coarse deposits were not observed and the fine particle deposits containing Zr compound were present. In double pulse electrolysis, since at low current density, the rate of hydrogen evolution decreases and Zn deposits without co-deposition of Zr compound, the continuous hydrogen evolution is suspended in some areas and the area of hydrogen evolution seems to become random. Although Zr compound concentrated at upper area of deposited films regardless of electrolytic method, it codeposited even at inner part with double pulse electrolysis. The corrosion current density in 3 mass% NaCl solution was the smallest for the films produced by double pulse electrolysis, comparing with films obtained by pulse electrolysis and constant current electrolysis. This is attributed to reduction reaction of dissolved oxygen being suppressed.

The effect of stability of austenite (γ) phase on Lüders-like deformation behavior of cold-rolled Fe-Ni-Al-C alloys was investigated by digital image correlation (DIC) analysis, magnetic measurements and electron backscatter diffraction (EBSD) analysis. In this study, cold-rolled Fe-23Ni-5.0Al-0.5C (mass%) alloy (23Ni alloy) and Fe-25Ni-5.0Al-0.5C (mass%) alloy (25Ni alloy) were used. The tensile strength increased and the total elongation decreased with decreasing Ni content. Lüders-like deformation after yielding was observed up to a nominal strain of approximately 0.04 for the 23Ni alloy and approximately 1.0 for the 25Ni alloy. The transformation from γ to martensite (α') with a specific crystal orientation relationship was observed during tensile deformation, and it was found that the volume fraction of α' during tensile deformation increased more easily in 23Ni alloy than in 25Ni alloy. In addition, the increment of α' phase in 25Ni alloy was higher during Lüders-band propagation than after the band propagation. These results suggested that change of the Lüders-like deformation behavior was due to the change in γ stability.

Ferritic stainless steels are used for automobile exhaust parts because of their high heat and corrosion resistance. Among them, parts located upstream near the engine, so-called hot-end parts, for example, exhaust manifolds, are required to show excellent heat resistance. Since thermal fatigue is induced by repeating heating and cooling with mechanical strain restriction, thermal fatigue resistance is one of the most important properties of upstream exhaust-parts materials.

In this study, the effect of Al addition on thermal fatigue deformation morphology was investigated for high heat-resistant ferritic stainless steel SUS444 which has been used for automobile exhaust parts. In contrast with the steel without Al addition, which fracture morphology in thermal fatigue under the maximum temperature of 1,173 K was necking, cracking was predominant in the steel with Al addition without necking. Al addition has the effect to prevent necking in thermal fatigue under the maximum temperature of 1,173 K due to solid solution strengthening by Al.

The relationship between melting temperature of multi-component chlorides and their ionic bond strength was studied. It can be used as a convenient method to know the melting temperature when thermodynamic information is lacking for the multi-component chlorides.