Viscosity measurements of a gas-liquid two-phase fluid (foam) with fine bubbles were conducted using a sphere pull-up method and the flow behavior in dam-break experiments was evaluated. The following results were obtained.

(1) Using known silicone oil, external forces were measured to determine the conversion constants under various sphere diameters and descent speeds. Subsequently, the viscosity of the foam was measured similarly. The results indicated that the foam exhibited shear-thinning behavior and could be classified as a pseudo-plastic fluid.

(2) The viscosity of the foam showed little variation between gas volume fractions of 0.4 and 0.65 but increased significantly near 0.8. This trend was consistent with the results obtained by Hatano et al. using a rotational viscometer.

(3) In the dam break experiments, the traveling distance of the foam was proportional to time for gas volume fractions between 0.65 and 0.85, while at 0.95, the initial flow velocity was slow and increased gradually.

(4) Using the relationship between viscosity and shear rate of the foam measured by the sphere pull-up method, 3-D numerical fluid flow calculations were performed under dam-break conditions. Since the calculated time for traveling to the bottom was shorter than that of the experiment, an inverse analysis was performed to obtain a relationship between viscosity and shear rate that was compatible with the experiment. As a result, it was found that the viscosity at high shear rate was underestimated by the sphere pull-up method.

Steelmaking slag contains a considerable amount of phosphorus, which is widely used in human society. Phosphorus recovered from steelmaking slag will provide a new resource, and reusing the steelmaking slag, from which phosphorus has been removed, in the steel manufacturing process reduces the total slag volume. In this study, phosphorus was separated from phosphorus-concentrated slag, which was produced through the oxidation of high-phosphorus hot metal using a small amount of steelmaking slag. The leachate of the phosphorus-concentrated slag was obtained by agitating the slag in citric acid at pH=3 using a mill pot containing mill balls. To separate phosphorus from the leachate by the precipitation of calcium phosphate, the pH of the leachate was increased by adding NaOH solution to increase the pH from 3 to 11, and by adding Ca(OH)₂ solution or Ca(OH)₂ powder to increase the pH from 3 to 11. The recovery ratio of phosphorus was over 75% for these methods. The P₂O₅ content in the recovered precipitates was over 30 mass%, which is higher than that in natural phosphorus ores. It is calculated that 50% of phosphorus in hot metal could be recovered as precipitates, and when the leaching residue was recycled for hot metal dephosphorization, the amount of slag emissions was reduced by 34% compared to the current hot metal dephosphorization operation. It is suggested that phosphorus can be recovered from steelmaking slag and slag emissions can be decreased through slag treatment processes such as slag reduction, dephosphorization, acid leaching, and precipitation.

In the point of view of reducing coke production cost and future resource depletion, it is necessary to produce high-strength coke from low-rank coal.

It is reported that high strength coke can be obtained by pulverizing, compacting, and carbonizing low-rank coal, non-or-slightly-caking coal. In this study, we research the effects of coal size and coal charging density on coke strength and coke density, and discuss the mechanism for the change of coke properties. Coal of 1.0 mm or less to 0.1 mm or less was compacted to 0.8 g/cm³ to 1.1 g/cm³, carbonized at 900°C, and coke strength and coke density were measured.

As a result, it was found that coke strength significantly increased by pulverizing to 0.1 mm or less and increasing the coal charging density. The effects of coal particle size and coal charging density on coke properties are examined. When the grain size of coal becomes finer, swelling is suppressed, and large pores and connecting pores of coke are reduced. As the coal charging density increased, the coke density increased due to the shortening of the distance between coal particles.

Casting experiments of Al–10 wt.%Cu alloy were carried out using an impreved Satou mold (iST mold). The mold was a rectangular parallelepiped (inner dimensions 30 mm^T × 50 mm^W × 140 mm^H), with a porous alumina plate on the wide side of the mold and a chill set at a height of 70 to 80 mm from the bottom. Four metal materials (stainless, steel, brass, and copper) with different thermal conductivities were used for the chill. To investigate the effect of bridging on the formation of macrosegregation, X-ray CT analysis of the macrosegregation distribution and morphology, observation of micro- and macro-structures, and analysis of temperature and solid fraction distribution were performed for samples obtained under each condition. Bridging formed near the chill under all conditions, and channels consisting of positive segregation and cavities were formed below it. The volume fraction of positive segregation decreased as the thermal conductivity of the chill material increased. In the samples using stainless and copper as chill materials, the volume fractions of positive segregation were 73.8% and 11.7%, respectively. Consequently, we confirmed that the bridging-formed conditions have a significant effect on the formation of macrosegregation.

In the peritectic solidification, the same solute has been ejected toward the liquid during the growth of primary and secondary phases and these two phases grow interacting with each other. In this study, the unidirectional solidification experiments by using binary Ag–Sn alloy have been performed to find the layered structure solidification, in which primary phase and secondary phase alternately grow in hyper-peritectic Ag–Sn alloy. In order to clarify the mechanism of the aforementioned solidification phenomena, the relationship between fractional solid and Sn concentration distribution obtained by FE-EPMA was examined by using the random sampling methods. Through some theoretical analysis, it has been estimated that solute convection due to the density difference between bulk and inter dendritic liquid could occur and the growth and decline of primary phase could be repeated periodically in the unidirectional solidification. Based on these results, a mechanism for the occurrence of the layered structure solidification induced by solute convection was proposed. Furthermore, it was confirmed that the layered structure solidification also occurs in hypo-peritectic under conditions that promote convection, revealing that the presence or absence of convection directly influences the occurrence of the layered structure solidification.

Sulfur is one of the five ubiquitous elements of steel, and the presence of sulfur reduces the performance of steel. Therefore, the sulfur content in steel must be strictly controlled. This paper focuses on the gravimetric method after separation of iron (JIS G 1215-1) specified in the Japanese Industrial Standards (JIS) as an absolute analysis method for sulfur content in steel. The precipitation formation process of BaSO₄ and the rinse process of the formed precipitate had a major influence on the recovery. In the formation process of BaSO₄, it was confirmed that the precipitation was almost completely formed under the conditions specified in JIS G 1215-1. However, the coexistence of manganese ions (Mn²⁺) significantly reduced the precipitation recovery. Ethylenediaminetetraacetic acid (EDTA) was effective for masking Mn²⁺. In JIS G 1215-1, the BaSO₄ formed is rinsed in two steps: first, barium chloride solution (BaCl₂) is used to remove foreign substances, followed by hot water to remove the BaCl₂. Mn²⁺ not only inhibited the precipitation of BaSO₄ but also reduced the recovery during rinsing with hot water. Sulfur recovery in the entire JIS G 1215-1 process exceeded 100% regardless of the addition of EDTA. This indicates loss of sulfur during the precipitation process much less contributed the recovery of sulfur in the total process of JIS G 1215-1.

In order to improve both performance and safety of lithium-ion batteries, we investigated the use of steel sheets which have a higher melting point than aluminum currently used for cell cases of lithium-ion batteries, for cell cases. First, a coating metal that can suppress Fe dissolution was selected, because corrosion resistance to battery electrolyte is important for battery cell cases. We found that Ni has high corrosion resistance to battery electrolyte, and that Ni-coated steel sheets can reduce the risk of short circuits due to decrease in Fe dissolution and re-deposition compared to non-coated steel sheets.

Next, the performance of the battery using Ni-coated steel sheet as the cell case was shown, and the discharge capacity after 500 cycles was the same as that of the battery using aluminum as the cell case, confirming that there is no problem with the battery performance.

For battery cell cases, it is also important to have superior high-temperature strength to suppress burnout in the event of thermal runaway. Ni-coated steel sheets have superior high-temperature strength compared to aluminum.

These characteristics of Ni-coated steel sheets are expected to be applied battery cell cases to produce batteries with superior performance and safety.

Super invar alloy, Fe–32%Ni–5%Co, is widely utilized in precision instruments due to its remarkably low thermal expansion coefficient. Additive manufacturing holds promise for fabricating complex-shaped components with this alloy. This study investigated the phase stability and thermal expansion properties of super invar alloy fabricated via Laser Powder Bed Fusion (AM sample), comparing them to those of conventionally cast material (Re-melt sample). Microstructural analysis indicates that the AM sample has a more stable austenitic structure, attributed to minimal micro-segregation. Furthermore, it was observed that the thermal expansion coefficient decreases consistently with higher cooling rates within the temperature range of 400–300 K. As a result, AM sample exhibits lower expansion coefficient and it maintains at lower temperatures.

The strengthening mechanism of ausforming in martensitic steels is believed to be due to the inheritance of dislocations in austenite by the subsequently transformed martensite. However, no studies to date have quantified the dislocation density before and after ausforming. In this study, the dislocation densities of Fe–5%Mn–C alloys were analyzed, and the relationship between hardening by ausforming and dislocation accumulation, as well as the effect of carbon on this relationship, were investigated. The hardness of ausformed martensite increased with the ausforming reduction in austenite, and the strengthening effect of ausforming increased with the addition of carbon. Similarly, the dislocation density of ausformed martensite increased with the ausforming reduction in austenite, and the dislocation accumulation by ausforming increased with the addition of carbon. Because the hardness of the ausformed martensite follows the Bailey–Hirsch relationship, the strengthening mechanism owing to ausforming could be explained by dislocation strengthening. To understand the dislocation accumulation process during ausforming, the dislocation density of austenite immediately after ausforming was measured by in-situ heating neutron diffraction. Consequently, the dislocation density of the ausformed austenite was not dependent on the carbon content, indicating that dislocations are not inherited in carbon-free steels. By contrast, in steels with sufficient carbon content, not only are dislocations inherited but additional dislocations are introduced during martensitic transformation.

A fundamental study on the axial crush performances of HSS (High Strength Steel) was carried out to clarify the effects of microstructures and mechanical properties on crashworthiness. Axial crush tests were performed to evaluate the crush performances of the HSS with different microstructures and mechanical properties and identify the fracture origin. The cracks were observed in the press formed area, and they worked as the fracture origin. The high λ (Hole expansion ratio) steel showed excellent crush performances by crack suppression. The crush deformation in the press formed area was simulated by the ORB (Orthogonally Reverse Bending) fracture tests and the crack suppression factors were investigated. Through the ORB fracture test, it was clarified that the reduction of the hardness gaps between phases and the refinement of the hard phases (Fresh martensite) were effective for suppressing cracks in the press formed area. These microstructures were obtained by the Q&P (Quenching & Partitioning) process for increasing λ. Therefore, it was found that the microstructural design for increasing λ also contributed to excellent crush performances.

New fracture process model of cleavage fracture initiated from cementite crack was proposed. In addition, the equation of propagation of cementite crack into the ferrite grain was developed based on the Brechet-Louchet model. This equation can reproduce not only ferrite size dependence of cleavage fracture stress that the Petch model can reproduce but both of test temperature dependence and strain rate dependence of fracture stress. Furthermore, in exchanging surface energy for grain boundary cohesive energy in the equation, grain boundary fracture stress can be also estimated.

Creep deformation and precipitation behavior of 9Cr–1Mo–V–Nb steel with excess nitrogen introduced by solution nitriding were investigated. Precipitation of Cr₂N phase was confirmed in addition to M₂₃C₆ and MX phases in the tempered microstructure. The creep strength of the steel was significantly reduced by solution nitriding, while the creep rupture elongation was increased. To characterize the complex precipitation behavior of the nitrogen-added steel, a machine learning-based clustering method of the multidimensional scatter diagram of the X-ray intensity of the alloying elements in each pixel of a STEM-EDS map was developed. Reduced number density of precipitates and enhanced coarsening kinetics of both Cr₂N and MX were proposed as the mechanism of weakening caused by excess nitrogen.