Hydrogen-enriched blast furnace ironmaking has emerged as one of the pivotal technologies for decarbonizing the integrated steelmaking route. To further investigate the hydrogen-rich reduction behavior of iron-bearing materials in blast furnaces, this study systematically examines the hydrogen-rich reduction reaction of basic pellets through interruption experiments combined with microstructural characterization and phase analysis. Experimental results demonstrate that the basic pellets achieved a 79.7% reduction degree in CO–N₂ atmosphere, which increased significantly to 93.7% with 16 vol% H₂, confirming hydrogen’s remarkable enhancement effect on the reduction index of basic pellets. In the initial of reduction, CO accumulates on the surface of pellets, resulting metal iron on the surface, while the interior is the initial Fe₂O₃ state. But hydrogen enhances the internal reduction degree. Hydrogen-rich promotes more thorough reduction of internal microparticles within basic pellets. XRD results indicate that in the later stage of CO reduction, the FeO peak of pellets is stronger. XRD fitting analysis demonstrate that FeO phase is 37.85% after 180 min reduction, and the FeO phase of pellets reduced by reducing gas concluding 8 vol% H₂ accounts for 14.79 wt%.

In direct reduction ironmaking process, CO₂ emissions, energy consumption, and the carbon content in direct reduced iron (DRI) are closely linked. Therefore, understanding the DRI carburizing behavior is essential. This study examined Boudouard reaction - one of the primary reactions - under pressurized conditions equivalent to those in commercial reactors. Experiments revealed a significant radial carbon gradient in DRI and a reaction rate peak at a temperature different from that in pure iron plates. In addition, a newly developed numerical model, based on detailed reaction mechanisms, reproduced this behavior and showed: 1. CO₂ retention causes the gradient and deviation from iron plate behavior, 2. Gas diffusion follows Fick’s law via molecular diffusion only, 3. Pores < 5 µm are inactive, and 4. Fe₃C acts catalytically equivalent to 12% Fe on a molar basis.

The compositional ranges of SFCA series and the phase equilibrium relationships were reevaluated in the iron-rich corner of the CaO–Fe₂O₃–Al₂O₃ system at 1240°C in air using powder and single crystal XRD as well as EPMA: The liquidus line was reexamined using the samples with initial compositions close to the liquidus line. The observed liquidus line was shifted to the Fe₂O₃ rich side from the previous one reported by the present authors. The liquidus compositions of the samples, the initial compositions of which were far from the liquidus line, may be affected by CF (CaFe₂O₄), CFF (Ca₂Fe_15.51O₂₅) and C₂F (Ca₂Fe₂O₅) precipitated during quenching. Some of the limits of compositional range of SFCA-I, SFCA-II and SFCA were determined by newly prepared samples with the three-phase equilibriums such as liquid + SFCA-I + hematite. It has been found that the Al₂O₃ concentration is the smallest for SFCA-I and the largest for SFCA: The Al/(Al + Ca + Fe) ranges from 5.61% to 17.55% for SFCA-I in equilibrium with a liquid phase, from 14.75% or even lower to 25.00% for SFCA-II and from 19.93% to 31.42% or even higher for SFCA.

It has been found that the phases of a sample having the initial composition of 10.04CaO-63.47FeO_1.5-26.49AlO_1.5 (mol%) equilibrated at the oxygen partial pressure of 0.1 atm and at 1390°C are SFCA-I and SFCA-III. The value of Fe²⁺/Fe in SFCA-III has been calculated to be 20.36% assuming that the structural formula of M₂₆O₃₆ (M = Ca, Fe, Al) is satisfied by the presence of Fe²⁺: (Ca²⁺_1−xFe²⁺_x)₆(Fe³⁺_1−yAl³⁺_y)₂₀O₃₆ (x = 0.57, y = 0.33).

The iron- and steelmaking industry accounts for approximately 14% of domestic CO₂ emissions in Japan. There are many difficult challenges to achieve net-zero emissions based on the conventional blast furnace process because it is already operated with high efficiency. One of the promising ironmaking processes aiming at net-zero emissions is the hydrogen reduction shaft furnace. However, one of the major issues in this process is the disintegration of iron ore pellets. however, its mechanism has not been clear yet. In this study, the disintegration mechanism of the pellet in the hydrogen reduction shaft furnace condition at 550°C was examined.

Under hydrogen reduction shaft furnace condition, disintegration of the pellet proceeds through the formation of fine particles (particle with the size of less than 0.25 mm) and intermediate grains (particles with the size of greater than 2.8 mm, and formed by volumetric fracture), similar to the behavior observed under blast furnace conditions. However, unlike in the blast furnace conditions, metallic Fe formed even at 550°C under hydrogen reduction shaft furnace condition. Furthermore, the RDI value continues to increase even if reduction degree exceeds 11%, where reduction from hematite to magnetite is completed. It suggests that the formation of metallic Fe may influence the formation of fine particles. Under hydrogen reduction conditions, cracks with lengths of several µm to tens of µm were observed in the magnetite phase surrounded by the metallic Fe phase. It is considered that cracks were primarily caused by the volume contraction associated with the formation of metallic Fe.

In industrial environments, the internal quality of continuously cast steel shapes is typically evaluated afterwards by means of macroetch testing. Nevertheless, this approach becomes increasingly difficult as the product dimensions grow larger. When process parameters change — for example, with an increase in productivity — it is advisable to have a virtual macroetch available to perform a preliminary quality assessment.

In the literature, models exist to predict porosity and microstructure of the final product; however, their validity has been tested only for very simple shapes. In this work, using a travelling-slice approach, a virtual macroetch model was developed for billets and blooms. Comparison with experiments shows that, in the case of billets, the approaches available in the literature provide accurate results. For blooms, however, an accurate prediction of porosity requires a modification of Niyama’s criterion, introducing a correction in the exponent q, while Hunt’s criterion remain applicable for microstructure.

Based on these results, the case of a beam blank cast at high speed was analyzed. The study confirmed the feasibility of the process, with only a limited increase in porosity and a slight reduction in the equiaxed area in the inner part of the beam blank.

In this study, neutron diffraction mapping was performed on linear friction welded joints of a 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate the distribution of residual stress, dislocation density and crystallographic orientation. Linear friction welding (LFW) was conducted under two applied pressures (100 MPa and 250 MPa). The welded interface primarily consisted of refined ferrite with minor retained austenite and martensite, suggesting that peak temperatures during welding exceeded the A₁ point (the eutectoid transformation temperature) and induced reverse transformation to austenite. However, the joint produced at 250 MPa exhibited a lower welding temperature. At the weld region, grains near the specimen surface were elongated along the oscillation direction (OD), whereas equiaxed grains appeared at the center in both thickness and width directions. Inhomogeneous microstructural distributions were observed near the interface along OD. Both joints exhibited high tensile residual stresses in all directions at the weld center, while compressive residual stresses developed near the surface in the direction perpendicular to the weld interface. The applied pressure had minimal influence on the overall residual stress distribution trend within the tested welding conditions. Dislocation density at the weld interface was higher than that in the base metal, and the increase was more pronounced under higher applied pressure. This is attributed to suppressed dynamic recovery caused by the lower welding temperature at higher pressure. Finally, strong texture formation was observed at the weld interface due to plastic flow during welding. The applied pressure had only a limited effect on texture development.

Microbial extracellular electron uptake (EEU) is central to bioelectrochemical processes and biocorrosion, yet its underlying mechanisms are not fully understood under microbially influenced iron corrosion. Here, we investigate how excess Fe²⁺ modulates EEU in Desulfovibrio ferrophilus IS5, a strain that causes severe anaerobic iron corrosion via outer-membrane cytochromes (OMCs)-mediated electron uptake. We show that IS5 grown with elevated Fe²⁺ exhibits substantially enhanced EEU. This enhancement arises through two complementary mechanisms: (i) increased abundance of functional OMCs via the upregulation of a cytochrome assembly protein, and (ii) an additional electron transfer route mediated by FeS nanoparticles precipitated on the IS5 outer membrane. This indicates that, during iron corrosion, when IS5 cells are found within thick layers of corrosion products and biofilms, they simultaneously utilize both OMCs and FeS nanoparticles to sustain high-rate EEU from iron under conditions of high Fe²⁺ concentrations and limited organic substrates. This study advances the mechanistic understanding of EEU-driven iron corrosion and highlights a potential avenue for manipulating bioelectrochemical systems.

To develop a high-accuracy fatigue life prediction model for AISI 316 and AISI 430 under combined axial and internal pressure multiaxial proportional and non-proportional loading conditions, the Bi-LSTM and Bi-GRU deep learning algorithms were employed. In addition, two conventional machine learning algorithms, namely random forest (RF) and support vector regression (SVR), were utilized for comparison. The obtained results indicate that the von Mises equivalent stress approach, as well as the RF and SVR models, failed to accurately predict fatigue life under such complex loading conditions. In contrast, the Bi-LSTM model achieved higher prediction accuracy for AISI 316, with almost all predicted data points aligning closely along the diagonal line, except for one outlier. On the other hand, the Bi-GRU model exhibited better predictive performance for AISI 430. Furthermore, 50 independent holdout splits were conducted for both Bi-LSTM and Bi-GRU models to analyze the RMSE distributions of the testing subsets. The results were found to be consistent with the predictive outcomes, confirming the reliability and stability of the developed deep learning models.

In body-centered cubic (bcc) iron (Fe), highly diffusible solute hydrogen (H) atoms are easily trapped at lattice defects, i.e., grain boundaries (GBs) and vacancies, where concentrations reach thermal equilibrium. The presence of H atoms can increase vacancy concentration under plastic deformation. Although molybdenum (Mo) additions mitigate hydrogen embrittlement (reducing elongation loss by H), the underlying mechanisms remain unclear. To address this gap, herein, the interactions of H atoms with additive atoms (carbon (C), nitrogen (N), and Mo) and vacancies in the bcc Fe lattice and at the Σ3 and Σ5 symmetrical tilt GBs were analyzed via density functional theory calculations. In the bcc Fe lattice, C and N atoms exhibited a stronger repulsion toward H atom than Mo atom. However, the higher solubility of Mo atoms is expected to reduce the overall H diffusion coefficient by reducing the H diffusion paths. C and N atoms promote vacancy formation, while Mo atom exhibit negligible interactions with a vacancy and do not reduce the vacancy formation energy. C and N atoms at the GB plane showed strong H repulsion, whereas Mo atom showed weak H repulsion. Thus, C and N atoms more effectively suppressed H segregation at the GBs. The effects of these additive atoms (C, N, and Mo) on the vacancy-trapping energy at the GBs were generally negligible. Finally, vacancy trapping at the GBs with an additive atom recovered the H-trapping energy to the value for the GB with only a vacancy.

Carbonation is a carbon capture, utilization, and storage (CCUS) technology aimed at extracting Ca and Mg from basic waste, fixing CO₂, and utilizing the resulting products (CaCO₃ and MgCO₃), while valorizing the unused resources. Steelmaking slag, with its high CaO concentration and large production volume, is a by-product with a high potential for carbonate recovery. In this study, we propose a cyclic indirect carbonation process consisting of (I) leaching of Ca and Mg from slag using HCl, (II) absorption of CO₂ using an alkaline solution, (III) precipitation of carbonates from the leachate using Na₂CO₃, and (IV) regeneration of HCl and NaOH from the wastewater using bipolar membrane electrodialysis. (I) and (III) were investigated in detail. Slag leaching at a final pH of 2.46 resulted in a leaching rate of 81.4% for Ca. However, Mg, Si, P, Al, Fe, and Mn were also leached at approximately 30%–60%. When the slag was leached at a final pH of 11.83, the Ca leaching rate was only 3.0%, but other impurities were hardly leached. When carbonates were precipitated from these leachates using Na₂CO₃, ochre-colored CaCO₃ powder with a purity of approximately 40% and containing many impurities in the slag was obtained from the leachate at a final pH of 2.46, while a white CaCO₃ powder with a purity of 97.1% was obtained from the leachate at a final pH of 11.83. These carbonates are expected to be useful raw materials for cement and papermaking, respectively.

The coke-oven wastewater contains high concentrations of ammonia, COD (chemical oxygen demand) and toxic compounds such as phenols, cyanides, and thiocyanate. This wastewater is one of the most toxic industrial wastewater. Although the activated sludge process has been applied to treatment of the coke-oven wastewater, the treatment was occasionally deteriorated by inhibition of toxic compounds. Especially, the nitrification step was sensitive to toxic compounds, nitrite (NO₂⁻) was often accumulated due to incomplete nitrification. Nitrite is toxic and has a negative effect on COD degrading bacteria. The complete nitrification was required for stable treatment.

In this study, aiming at simultaneous removal of ammonia and COD from the coke-oven wastewater, a bench-scale nitrification/denitrification plant was operated. By long-term acclimation and the addition of an iron source, the complete nitrification was stably occurred for about 8 months, and a nitrogen removal efficiency of nearly 70% was achieved. In addition, COD in the influent was consumed as an organic source for denitrification, and the addition of an organic source was able to be minimized.

The scope of Ar+N₂ TIG welding, for which a few percent of nitrogen gas contents are mixed into argon shielding gas, is expanding toward realization of a carbon-neutral society. However, spattering is sometimes generated during TIG welding under Ar+N₂ shielding gas. Earlier studies have suggested that gas generation and rapid gas growth within the weld pool generate spatter. Nevertheless, no direct causal relation between gas generation in the weld pool and spatter generation has been clarified. Furthermore, the quantitative growth rate of the bubbles which generate spatter also remains unclear. For this study, we performed high-speed direct observation of the weld pool interior using quartz glass and quantitative analysis of the nitrogen content in the weld. The findings revealed the relation between gas generation and spatter in Ar+N₂ TIG weld pool. During Ar+5%N₂ TIG welding, a large amount of dissociated nitrogen was absorbed into the weld pool through the arc plasma space, exceeding the nitrogen solubility in the weld pool and leading to gasification. The apparent radius of the bubble grew transiently at approximately 0.5 m/s immediately before spatter ejection. Spattering then occurred when the grown bubbles were released into the atmosphere. These results indicate that the nitrogen solubility, which is material-dependent, serves as the threshold for spatter generation during TIG welding.