This study has analyzed the growth and removal mechanisms of Al₂O₃, MgO, MgAl₂O₄, ZrO₂, SiO₂, and Ti₃O₅ inclusions in molten steel formed through the addition of various deoxidizing elements by dividing them into single inclusions and cluster inclusions resulting from the agglomeration of these inclusions with a focus on the kinetics. Additionally, we have evaluated the maximum particle diameter of cluster inclusions from both thermodynamics and agglomeration force perspectives to examine the agglomeration properties and mechanisms of various inclusions. The growth mechanism of various single inclusions, measuring several micrometers in diameter and suspended in molten steel, is governed by Ostwald ripening with collision agglomeration due to Brownian motion and turbulent stirring. Contrarily, cluster inclusions with diameters of 10 µm or more float in molten steel agglomerate with suspended single inclusions. Depending on the inclusion type, they also agglomerate with other clusters along their floating path, growing larger and undergoing floating separation. Furthermore, the agglomeration strength of various inclusions in molten steel follows the order MgO < Ti₃O₅, SiO₂ < MgAl₂O₄ < ZrO₂ < Al₂O₃. The kinetic mechanism of agglomeration growth is explained in a unified manner by the interparticle interactions of agglomeration force driven by cavity bridge forces.

Micro-yielding occurs during macro-yielding in the steel, or polycrystalline material. In this phenomenon, some grains start to transform preferentially at lower strain, or the steel has preferentially deformed grains. However, this phenomenon has mostly been studied in uniform-grained steel so that the effect of duplex-grains is not clear. In this study, preferentially deformed grains during micro-yielding in duplex-grained austenitic steel are investigated. Rotation angle of every grain as deformation is analyzed with SEM-EBSD. Every preferential deformed grain has no trend for grain size and Schmid factor separately. In case grains which are in contact with a preferential grain have larger size and larger/smaller Schmid factor than it, it may be affected by around grains into deforming (Case I). On the other hand, in case grains which are in contact with a preferential grain has smaller size than it, it has larger size and larger Schmid factor (Case II).

To elucidate the mechanisms of deformation and a state of plastic stability at the front of Lüders bands during a tensile test, metastable austenitic transformation-induced plasticity (TRIP) steels with different dislocation densities and ferritic steels were characterized via macroscopic-DIC-based stress–strain investigations and scanning electron microscopy (SEM). A direct correlation between stress–strain curves and measured strain distributions in the tensile specimen indicated that the Lüders front represents a transition region from a state of plastic instability to one of stability, whereby a general rule relating the Lüders strain (Δε_L^*) and increments in the true stress in the Lüders band (Δσ_L^*) to a lower yield stress (σ_y0^*) can be described as σ_y0^*=Δσ_L^*Δε_L^* irrespective of the amount of deformation-induced martensite in the band or crystal structure of the steel. The inclination angle of the Lüders front with respect to the tensile direction changed from 55° to 90° with a reduction in the measured strain ratio (−ε_yy/ε_xx) in the Lüders band, and the change agreed with the tendency calculated by the plasticity model assuming the pure shear deformation under the minimum shear strain criterion. SEM observations of the sheet surface and the front cross-section in the TRIP steel revealed the formation of multiple inclined ~20 μm-wide shear deformation zones that accompanied a reduction in thickness. All the observed geometrical characteristics of the Lüders front are qualitatively explained by minimizing the misalignment from the fixed tensile axis caused by shear mode deformation.

This study explores a method for the synthesis of formic acid from CO₂ through the utilization of biomass-derived bio-oil, specifically focusing on leveraging levoglucosan (LGA) as a key intermediate. Formic acid has the potential to be a feedstock for the synthesis of oxalic acid, a key chemical compound in an iron-making method proposed by the authors. The research investigates the pyrolysis of lignocellulosic biomass, emphasizing the effects of oxalic acid washing on the yield of LGA and its content in bio-oil. By employing a fixed-bed pyrolyzer, the study demonstrates a significant increase in LGA yield when using oxalic acid-treated biomass compared to untreated sample. The pyrolysis with a fluidized-bed pyrolyzer successfully prepared bio-oil rich in LGA during 30 min of continuous operation. Additionally, the produced bio-oil is applied in a CO₂ alkaline hydrothermal conversion process to synthesize formic acid, highlighting the potential of LGA as both a reducing agent and a formic acid precursor. The findings indicate that the LGA-rich bio-oil not only enhances the formic acid yield but also exhibits superior performance compared to conventional reducing agents such as glucose. The study also considers challenges associated with improving CO₂ conversion efficiency, suggesting that the application of bio-oil could be a promising pathway for sustainable CO₂ utilization. The results pave the way for further optimization of bio-oil production and its integration into carbon capture and utilization (CCU) processes.

Assuming that heat is transported by lattice vibrations (phonons) in silicate glasses, their thermal conductivity is correlated with the product of sound velocity, volumetric heat capacity, and phonon mean free path (MFP). The sound velocity and heat capacity have been studied extensively, but the origin of the composition-induced variation in the MFP remains unclear. The present study investigated MFP in M_2/nO–SiO₂ (Mⁿ⁺: Li⁺, Na⁺, Ca²⁺, Sr²⁺, or Pb²⁺) glasses with a variation of M_2/nO content. The MFP of the silica glass decreased with the addition of M_2/nO. The effect of the type of metallic cation on the MFP was minimal for the selected alkali and alkaline-earth silicate glasses. By contrast, the MFP of lead silicate glasses was higher than those of alkali or alkaline-earth silicate glasses when the metallic cation contents were comparable. Previous studies have demonstrated that alkali and alkaline-earth cations act as nonframework species that break the silicate network structure, whereas lead cations have inconclusive structural roles. Our data indicate that lead cations partly act as framework cations and that phonons tend to be scattered near nonframework cations in silicate glasses. Thus, the phonon MFP is a useful parameter for determining the structural role of metallic cations in silicate glass via phonon propagation.

This study systematically investigates the catalytic performance of Ni‐supported metal oxide catalysts in CO₂ methanation, focusing on seven supports: ZrO₂, α-Al₂O₃, γ-Al₂O₃, MgO, TiO₂, ZnO, and CeO₂. In response to carbon utilization demands, CO₂ methanation, converting CO₂ and H₂ into synthetic methane, provides a promising route for renewable fuel production and energy storage.

An integrated approach of experimental evaluation and quantum chemical calculations was employed to examine adsorption stabilities of key intermediates (e.g., OH, OCHO, and other species) and to correlate these findings with catalytic activity. Experimental results indicated that ZrO₂ achieved the highest CO₂ conversion (49.2%) and CH₄ selectivity (73.5%), followed by α‐Al₂O₃ (46.0%) and CeO₂ (42.9%), while MgO displayed moderate performance. In contrast, TiO₂ and ZnO were nearly inactive under the tested conditions. Computational findings confirmed these observations, demonstrating that adsorption energy and bond order are strong predictors of efficiency.

Notably, ZrO₂ and CeO₂ were predicted to stabilize multiple reaction pathways, highlighting their versatility; Computational results provided insight into α‐Al₂O₃'s high activity in specific routes. By comparing single‐metal‐atom and twelve‐metal‐atom models, it was shown that smaller systems capture essential trends, thereby reducing computational requirements.

In conclusion, these results illuminate the critical role of adsorption stability in determining CO₂ methanation performance. Optimizing electronic properties and adsorption characteristics is crucial for enhancing catalytic efficiency. The combined experimental-computational analysis provides a basis for designing Ni‐supported metal oxide catalysts that advance sustainable CO₂ utilization and energy solutions. These findings offer valuable guidelines for optimizing catalyst design and improving catalytic efficiency for industry.

For reducing CO₂ emissions from blast furnace, carbon recycling blast furnace has been proposed. In carbon recycling blast furnace, reducing agents are synthesized from CO₂ by carbon recycling technology and injected into blast furnace. It has been reported that by synthesizing methane from CO₂ in the blast furnace gas and using it as a reducing agent, CO₂ emissions could be reduced by about 30 % compared to conventional blast furnace. However, it has not been investigated what type of reducing agent is suitable for carbon recycling blast furnace. Therefore, this study aims to examine what reducing agents are effective for CO₂ emission reduction of carbon recycling blast furnace. First, candidate chemical species for the reducing agent of carbon recycling blast furnace were investigated and extracted. Then, the amount of carbon consumption of carbon recycling blast furnace when different candidate reducing agents are injected into carbon recycling blast furnace was evaluated by using Rist diagram analysis. The effect of blast oxygen concentration on the amount of carbon consumption were also evaluated. Based on these results, it was clarified that the amount of carbon consumption of carbon recycling blast furnace is mainly affected by the calorific value of partial combustion of reducing agent and blast oxygen concentration. It was found that by using hydrocarbons with higher calorific value of partial combustion than 4000 kJ/kg as reducing agents of carbon recycling blast furnace, carbon consumption and CO₂ emissions could be reduced by up to 40 % compared to conventional blast furnace.

The effect of χ phase precipitated at the grain boundary of matrix on the high temperature mechanical properties of ferritic Fe-Cr-Ni-Al-Mo alloys containing nano-sized B2-type NiAl precipitates was investigated. It was found that the grain boundary of Fe-22Cr-6Ni-6Al-3Mo alloy was covered with the χ phase approximately 95% by a heat treatment at 800°C for 50 h. However, the average particle diameter of the NiAl precipitates increases to approximately 300 nm during this heat treatment. We found that the NiAl precipitates can be refined to approximately 27 nm by additional heat treatment above the dissolution temperature of the NiAl precipitates followed by air cooling. The alloy with nano-sized NiAl precipitates and the χ phase exhibits a yield stress of 235 MPa at 700°C. The suppression of intergranular fracture by grain boundary strengthening caused by the χ phase and precipitation strengthening due to the nano-sized NiAl precipitates are responsible for the high strength of the alloy at high temperatures.

The effect of dislocation density on the σ phase precipitation behavior in KA-SUS304J1HTB was investigated. The specimen was pre-strained by room-temperature uniaxial tensile test and subjected to ageing at 700℃. The number density and area fraction of the σ phase after ageing increased with the amount of pre-strain. On the other hand, the pre-strain had no significant effect on the average σ phase diameter. Electron backscatter diffraction (EBSD) analysis revealed that the geometrically necessary dislocation (GND) density was increased with the amount of pre-strain. Moreover, the GND density of the pre-strained specimens showed little change after the ageing. The EBSD analysis also revealed that the GND density was significantly higher around the grain boundaries compared to the grain interior. Using the GND density around the grain boundaries in the pre-strained specimens, the change in the number density of the σ phase during ageing was calculated based on the classical nucleation theory. The calculated number density of the σ phase showed good agreement with the experimental results. This result implies that the effect of the pre-strain on the number density of the σ phase after ageing can be explained by the change in GND density around the grain boundaries.

In this study, influence of crystal structure and chemical composition for Silico-Ferrite of Calcium and Aluminum (SFCA) on its reducibility are examined. Eight types of the powder samples containing SFCA and SFCA-I phases were prepared using chemical reagents by the heat treatments in air. The samples were heated up to 800℃ in the different atmospheres of CO–CO₂–H₂–H₂O systems. The reducibility of the samples was evaluated using the peak intensity ratio identified by XRD before and during the reduction experiment. The intensity of SFCA peak is not decreased up to 700℃ in CO–CO₂ atmosphere, whereas the intensity become weak in CO–CO₂–H₂–H₂O atmosphere. The intensity of SFCA-I peak is decreased above 500^oC in all atmospheric condition and the reduction reactions are enhanced by the addition of H₂–H₂O gas. Decrease in intensity of SFCA peak is independent of Fe composition, whereas that of SFCA-I is decreased with decreasing Fe concentration. The difference in reducibility is attributed to the difference in the crystal structure of multi-component CF. SFCA and SFCA-I are composed of pyroxene and spinel units. Since the pyroxene unit contains more gangue minerals than spinel unit, it implies that the pyroxene unit shows low reducibility than the spinel units. Since SFCA-I contains more the spinel units than SFCA, SFCA-I is easily reduced than SFCA.

Reduced Multicomponent Calcium Ferrite was analyzed using STEM-EDS(scanning transmission electron microscope - energy dispersive spectrometer) and 3DAP(three-dimensional atom probe) in order to clarify the reducibility of SFCA(silico-ferrites of calcium and aluminum) based on the microstructure analysis. The morphological observation and crystal structure analysis using STEM-EDS revealed that the amorphous Ca-Si-O oxides, spinel phase (Fe,Mg)(Fe,Al)₂O₄ and brownmillerite phase (Ca,Fe)₂(Fe,Al)₂O₅ were formed in the metallic iron obtained by the reduction of SFCA. Since the relatively reducible spinel phase was observed after reduction, it is suggested that the formation of spinel phase (Fe,Mg)(Fe,Al)₂O₄ by the dissolution of Mg into spinel phase affect the reducibility of SFCA. It was also found that each oxide was dispersed in metallic iron in granular form, either singly or in complex form. The three-dimensional analysis by performing 3DAP clarified that the presence of the Fe-O enriched region with a width of about 2 nm existed at the interface between amorphous Ca-Si-O oxide and metallic iron. This result suggests that the morphology of amorphous Ca-Si-O oxides affect the reducibility of SFCA.

The declining quality of iron ore fines and increasing re-use requirement of steelmaking slag have led to higher Al₂O₃ content in sinter products. High grade concentrated hematite ore (concentrate) has been emerged as a potential solution for reducing Al₂O₃ levels of sinter. However, research regarding on the melting and assimilation behavior of concentrates in sintering process is limited. On the other hand, our previous work demonstrated that Parallel Granulation with Inclined Mixing of Limestone, based on the creation and mixing of pseudo-particles with high and low CaO/Fe₂O₃ ratios, can improve the sinter strength and productivity. To investigate the melting and assimilation characteristics of concentrates, we conducted melt dripping tests various kind of iron ore, revealing that adhesive layers with high concentrate content have low melt retention capacity. Furthermore, sinter pot tests under single granulation condition showed that when a large amount of concentrate is blended, fragile sinter cake is formed due to insufficient melting and assimilation. Sinter pot tests using Inclined Mixing of Limestone demonstrated that melting and assimilation are promoted by positioning concentrate near abundant melt sources.

REMO-tec, developed by Nippon Steel, is the sintering technique of re-igniting sintering packed bed at certain intervals after first ignition. This method improves sinter yield while maintaining high reducibility, thereby making REMO-tec a technology that contributes to reduce CO₂ emissions in both sintering and blast furnace operations. This study aims to investigate the effects of re-ignition and coke breeze reduction on the mineral phase and pore structure of sintered ore through pot tests, providing a comprehensive evaluation linked to sintering operational parameters. Sinter pot tests were conducted with a 130 mm layer of raw materials, focusing on the upper part of the sintering layer. Experimental conditions included a base condition with single ignition and REMO-tec with re-ignition under three levels of coke breeze blending ratios (4.1, 3.3, and 2.9%). Microstructure observation and pore structure analysis were conducted using an optical microscope and image processing, respectively. REMO-tec extended the high-temperature holding time while maintaining the maximum bed temperature, leading to the formation of an acicular calcium ferrite under low coke conditions (3.3 and 2.9%) with a peak temperature of approximately 1250℃. Additionally, pore structure analysis revealed that the reducibility of sintered ore correlates with the volume of pores smaller than 200 µm. Consequently, producing high-FeO sintered ore with an acicular calcium ferrite matrix and a large volume of pores smaller than 200 µm through REMO-tec under low bonding agent conditions is the most desirable approach for balancing sintering operational parameters and reducing CO₂ emissions in the ironmaking process.

In this study, the method to extract multi-component calcium ferrite (CF) into actual iron ore sinter is proposed and its reducibility is investigated under N₂-CO-CO₂ atmosphere. Actual iron ore sinter are pre-reduced at 500°C for 3 h in N₂-CO-CO₂-H₂-H₂O atmosphere and then sample particles containing mainly multi-component CF are successfully obtained through crashing and wet magnetic separation. In the isothermal reduction at 700-800°C, the reduction rate shows positive correlation with compositions of SFCA-I and SFCA-III up to early stage of reduction, and the negative correlation is obtained with SFCA. However the relationship is reversed, for example at 750°C for approximately 90 s. After approximately 380 s, there is no longer any correlation between SFCA and the reduction rate. It indicates that SFCA-I and SFCA-III are already reduced to intermediate products up to 90 s and the reduction of SFCA affects the reduction rate up to 360 s at 750℃. In the heating reduction using in-situ XRD, the formation of wustite is identified along with the decrease in the intensity of multi-component CF from around 600°C. The intensity of SFCA-III decreases from around 550℃ and disappears at 760℃, whereas the SFCA-I decreases more gradually. It is known as the multi-component CF consists of series of spinel and pyroxene structure. Since the proportion of S units is SFCA-III > SFCA-I > SFCA, it implies that the reduction of Fe ions advances in S units than in P units.

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.

In this study, the influence of Fe²⁺/Fe³⁺ ratios in SFCA-I on its reducibility are examined. Five types of powder samples containing SFCA-I with different Fe²⁺/Fe³⁺ ratios were prepared using chemical reagents by solid phase reaction at high temperature. The samples were heated up to 800℃ in the different atmospheres of CO-CO₂-H₂-H₂O systems. The reducibility of the samples was evaluated using the integrated intensity ratio identified by XRD before and during the reduction experiment. The integrated intensity ratio of SFCA-I is not decreased up to 700℃ in CO-CO₂ atmosphere, whereas the intensity become weak in CO-CO₂-H₂-H₂O atmosphere. The integrated intensity ratio of SFCA-I remains at 800°C under CO-CO₂ atmosphere. On the other hands, the integrated intensity ratio disappears under the CO-CO₂-H₂-H₂O atmosphere. The increase in the Fe²⁺/Fe³⁺ ratio in SFCA-I leads to the increase in the concentration of Fe in SFCA-I and significant decrease the integrated intensity under different reducing gas conditions at 750℃. The increase in the amount of Fe²⁺ may lead to enter Fe²⁺ into the spinel unit, and this may contribute to the reduction of SFCA-I.

Conventionally, it has been known that the product yield of the upper part of the sintering layer is extremely low, because of the heat loss caused by transferring heat toward the space above sintering layer, and of the large amount of unburned carbon in upper sintering layer.

As a countermeasure, REMO-tec (Re-ignition Method for Optimization of Total Energy Consumption) has been developed. Here, REMO-tec, is the sintering technique of re-igniting sintering packed bed at certain intervals after first ignition. This method has an effect on improving sinter yield with maintaining high sinter reducibility.

This paper focuses on gas flow rate control between first ignition and re-ignition for the purpose of further improving product yield.

It has been clear that certain decrease of gas flow rate between these two ignitions, has an effect on increasing heat storage amount in coke combustion zone at re-ignition caused by controlling vertical position of coke combustion zone.

This method has been applied in Kimitsu No.3sinter plant. Product yield improves by 0.3% with increasing high temperature holding time.

The reduction disintegration index (RDI) of sintered ore, which is the main raw material of blast furnaces, greatly affects blast furnace operation. In order to improve RDI without deteriorating the reducibility index (RI), sintered ore having a CaO concentration of 20 mass%, which is higher than the conventional 10 mass% when using porous Australian iron ore, was produced, and its effects on the mineral structure, porosity, RI and RDI were evaluated. In the sintered ore having a CaO concentration of 20 mass%, hematite decreased and calcium-ferrite (sum of other component system calcium-ferrite and binary calcium-ferrite), the SFCA-I/SFCA ratio and porosity increased in comparison with that having a CaO concentration of 10 mass%. When Australian iron ore was used as a raw material for sintered ore, RI increased in sintered ore having a CaO concentration of 20 mass% compared with the one having a CaO concentration of 10 mass%. In addition, RDI was improved in the sintered ore having a CaO concentration of 20 mass% compared with the that having a CaO concentration of 10 mass%. This is due to the formation of binary calcium-ferrite instead of secondary hematite, which deteriorates RDI.

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 this study, linear friction welding is applied to join JIS-S45C medium carbon steel with ferrite and pearlite structures at temperatures above and below the A₁ point. Additionally, low-strain-rate tensile tests are conducted both in air and with a cathodic hydrogen charge to evaluate the hydrogen-embrittlement susceptibility of the linear friction-welded joints under both joining conditions. Results of hydrogen thermal-desorption analysis show that the hydrogen-charging conditions in this study simulated atmospheric corrosion conditions. The joining zone of the above- A₁ joint comprises fine martensite and ferrite, whereas that for the below- A₁ joint comprises ultrafine ferrite and cementite. In air tensile tests, both joints fractured in the base-metal region, thus suggesting the high reliability of the joints. In the hydrogen-charged tensile test, the above- A₁ joints exhibit premature fracture at the joining zone. By contrast, the below- A₁ joints exhibit base-metal fractures, thus suggesting that the joints are highly reliable in a hydrogen environment. Fracture-surface observations show that the above- A₁ joints exhibit cleavage fractures in the martensite-dominated region. Tensile tests on heat-treated martensite S45C specimens show that their fracture strength decreased significantly in a hydrogen environment. Therefore, the joint fracture is due to the significant decrease in the fracture strength of martensite formed in the above- A₁ joints in the hydrogen environment. The linear friction-welded medium carbon steel joints below the A₁ temperature can ensure reliability even in a hydrogen environment.

Multi component calcium-ferrites (CFs) including in iron ore sinter are key component of sinter properties, such as strength and reducibility. Those in a sinter are crystallized from oxide melts and form various morphologies such as columnar, needle, and fine textures depending on the formation process. Ca₂(Fe,Ca)₆(Fe,Al,Si)₆O₂₀ (SFCA), Ca₃(Ca,Fe)(Fe,Al)₁₆O₂₈ (SFCA-I) and SFCA-III phases are representative multicomponent CFs, which are included in a sinter. Those texture and types of the crystal structure are not matched one by one. Since their compositional ranges and chemical properties have not yet been fully clarified, and they have micron ordered grain size, it is difficult to determine CF phases only by EPMA chemical composition analysis. In this study, phase determination of CFs in sinter was conducted by Electron backscatter diffraction (EBSD) analysis, which has better spatial resolution than Electron Probe Micro Analyzer (EPMA). Needle like CFs in the sinter with size of several microns were analyzed and confirmed presence of SFCA, SFCA-I and SFCA-III with the needle like texture. Crystal grains determined as SFCA showed higher Si content compared to those of SFCA-I, and this result is consistent with phase diagram. Mg concentration of SFCA-III found in sinter was in the range of 0.6－2.6mass%, which was lower than that of previously reported single crystal structure analysis sample.

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.

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.

The reducibility and mechanical properties of iron ore sinter in blast furnace is critical to effective plant operation. The reduction reaction of sinters progresses heterogeneously owing to microstructures with various mineral phases and pore networks. The reduction process was investigated by semi-microbeam synchrotron X-ray multimodal analysis. Heterogeneous chemical state evolution of Fe and trigger sites of crack formation were visualized using two-dimensional Fe K-edge X-ray absorption near-edge structure analysis and were discussed based on reduction gas transfer. The elemental composition map and X-ray diffraction microanalysis were also combined to reveal the microprocesses during the reduction, such as calcium ferrite decomposition and crystal grain growth.

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.

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.

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.

Friction stir welding (FSW) was applied to a 10 mm-thick plate for the Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy. A sound FSW joint was obtained successfully without macro-defects such as groove-like defects and tunnel holes. However, small pores with diameters of 1–5 μm were formed owing to the wear of the FSW tool during the FSW. The decrease in the heat input suppressed the tool wear. Consequently, the distribution of small pores was limited to the border of the stir zone at the advancing side under smaller heat input conditions. The stir zone of the FSW specimen produced at 125 rpm showed a higher tensile strength of 759 MPa owing to the grain refinement and the high elongation of 50% compared with the base metal. In addition, the stir zone exhibited a remarkable fatigue life of 9,723 cycles. This was higher than that of the base metal (8,908 cycles). Grain refinement occurred by discontinuous dynamic recrystallization (DDRX) via high-angle boundary bulging and direct nucleation in the high-dislocation area. The increase in the heat input suppressed the DDRX owing to the promotion of dynamic recovery.

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.

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.

To reduce the reducing agent ratio and CO₂ emissions in blast furnace operation, it is important to control the material structure of sintered ore, which affects its metallurgical and mechanical properties. Multicomponent calcium ferrites (also called CF or SFCA (silico-ferrite of calcium and aluminum)), which is a type of melting and solidification structure, has attracted considerable interest recently, and the chemical composition and crystal structure of each CF have been researched. Although the crystal structure of CF has conventionally been analyzed mainly by XRD, the atomic arrangement could not be observed directly. Therefore, in this study, CF was investigated at the atomic level by scanning transmission electron microscopy (STEM). This research revealed that acicular CF, which was previously understood to be SFCA-I, has a SFCA (≠ SFCA-I)structure. It was also found that columnar CF had a non-periodic SFCA structure induced with a magnetite-like structure. Furthermore, a CF in which SFCA and SFCA-I were alternately stacked repeatedly was also discovered. This research clarified the fact that CF has a non-periodic structure at the atomic level.

The effect of Al₂O₃ on the compositional region of silico-ferrite of calcium and aluminum (SFCA) and the liquid phase and the phase equilibria, including SFCA, was investigated in a CaO-SiO₂-Fe₂O₃-5mass%Al₂O₃ system at 1240 ^°C in air. To obtain the desired composition, reagent-grade CaCO₃, SiO₂, Fe₂O₃, and Al₂O₃ powders were weighed, mixed, and equilibrated at 1240 ^°C in air. Each obtained sample was divided into two parts: one was pulverized into a powder and analyzed by XRD, and the other was subjected to microstructural observation and compositional analysis using EPMA. The results revealed that the compositional region of SFCA lies on the CF₃-CA₃-C₄S₃ plane and is C/S = 2.77–7.60 for 5 mass% Al₂O₃. Compared with the SFC composition region for 0 mass% Al₂O₃, the compositional range of SFCA extended in the CF₃-C₄S₃ direction, suggesting that the addition of Al₂O₃ contributes to the stability of SFCA. Furthermore, the liquid-phase region was divided into a ferrite melt with a high Fe₂O₃ concentration and a silicate melt with a high SiO₂ concentration, both of which shifted to the lower Fe₂O₃ side compared to the liquidus isotherm in the CaO-SiO₂-Fe₂O₃ system. Unlike CaO-SiO₂-Fe₂O₃, SFCA-I (SFC-I) was observed in the CaO-SiO₂-Fe₂O₃-5mass%Al₂O₃ system, thus indicating that the addition of Al₂O₃ contributes to the stability of SFCA-I.

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.

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.

Conventionally, it has been known that the product yield of the upper part of the sintering layer is extremely low, because of the heat loss caused by transferring heat toward the space above sintering layer, and of the large amount of unburned carbon in upper sintering layer.

As a countermeasure, REMO-tec (Re-ignition Method for Optimization of Total Energy Consumption) has been developed. Here, REMO-tec, is the sintering technique of re-igniting sintering packed bed at certain intervals after first ignition. This method has an effect on improving sinter yield with maintaining high sinter reducibility. This effect leads to improving sinter reducibility without decreasing sinter yield by decreasing control of coke breeze content in sinter mixture.

This paper focuses on coke combustion efficiency as combustion ratio of carbon in coke breeze for considering improvement of sinter yield through sinter pot test. Here, carbon combustion ratio is defined as proportion of actual heat generation at combustion to ideal heat generation as complete combustion (C+O₂→CO₂) of all carbon in coke. And it can be calculated based on component analyses of exhaust gas.

As the result, it was confirmed as shown bellows.

1) By re- ignition, the unburned coke remaining in the upper layer of the sinter packed bed was burned, which has a role of extending keeping time over 1200℃ especially in the upper layer of sinter packed bed.

2) Due to the effect of 1), the increasing amount of heat supply at “REMO-tec” case was equivalent to the same as the experimental case of increasing coke breeze content, at which increasing heat amount at blending coke breeze content was four times larger of the heat amount at re-ignition. (For a 430 mm layer pot test)

3) In addition, since the re-ignition heat is donated to the upper layer (surface layer), the amount of heat consumption in the upper layer of the sinter packed bed increases and the amount of heat consumption in the lower layer decreases compared to the case of increasing coke breeze content, which results in decrease of the difference between heat consumption in upper layer and that in lower layer.

In addition, these effects have been also confirmed at the commercial sinter plant.

A fundamental study on the axial crush performances of HSS (High Strength Steel) was carried out to clarify the effects of microstructure 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 origins. The cracks in the press formed area were observed and the cracks led to the fractures. The high λ (Hole expansion ratio) steel showed excellent crush performances by crack suppression. Crash 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 occurred 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.