Gigapixel Fe K-edge imaging XAFS was developed to visualize iron ore sinter over a cm-scale field of view with submicron lateral spatial resolution. By applying singular value decomposition to XANES image stacks, Fe chemical phase maps were obtained for sinter specimens exhibiting distinct microstructures classified as relatively low- and high-temperature sintering textures. The improved spatial resolution enabled direct interpretation of fine sinter textures, including individual hematite grains and acicular calcium ferrite, without the auxiliary optical microscopy required in our previous study. In addition, the polarization dependence of hematite XANES was used to obtain hematite crystal orientation maps. Comparison with EBSD showed that the imaging XAFS orientation contrast was consistent with the crystallographic orientation observed by EBSD. The orientation maps revealed that skeletal hematite forms crystallographically coherent domains across apparent gaps between branches, which is consistent with growth from dendritic hematite. This orientation information further enabled the segmentation of primary and secondary hematite. The results demonstrate that gigapixel imaging XAFS provides simultaneous chemical-state and orientation-sensitive information for microstructural interpretation of iron ore sinter.

The magnetic properties of high magnetic induction grain-oriented silicon steel are closely related to the contents of Al and Ti and the characteristics of oxide inclusions. To realize the synergistic control of Al and Ti contents and oxide inclusions in the steel, thermodynamic and kinetic theoretical prediction models were established in this study, and the composition of the CaO-SiO₂-Al₂O₃-MgO slag system was optimized via high-throughput calculations. The effect of MgO content on the low-melting point region of the slag system was analyzed using FactSage 8.3 software, and the optimal MgO content was determined to be 6%–8%. Thermodynamic models for slag-steel equilibrium and mathematical models for inclusion separation and dissolution were established to reveal the regulation mechanisms of basicity and CaO/Al₂O₃ ratio on the contents of Al and Ti as well as inclusion behavior. Finally, the optimal refining slag composition was determined as follows: CaO=46~52%, SiO₂=18~24%, Al₂O₃=18~24% and MgO=6~8%. Industrial test verification showed that this slag system could stably control the soluble aluminum content in steel at around 0.029%, with aluminum loss less than 0.0030%, residual Ti content less than 0.0020%, and total oxygen content reduced to 0.0006% to 0.0007%. The inclusion number density was within 5 particles/mm², with an average size of approximately 1.7 μm, mainly composed of SiO₂-rich oxides, indicating a significant improvement in molten steel cleanliness. Correspondingly, heats refined by the optimized slag exhibit superior magnetic properties, featuring low core loss of 0.819–0.823 W/kg and high magnetic induction of 1.924–1.925 T.

In laser powder bed fusion (L-PBF), near-net-shape products are fabricated through the repeated alternation of powder spreading on the build platform and selective melting/solidification by laser scanning. The thermal history during the L-PBF process determines the microstructure and mechanical properties of the built sample. Previous studies have reported that the thermal history is influenced not only by laser scanning parameters, but also by the geometry of the build. In this study, a bipyramidal sample was fabricated from SUS304L powder to understand the relationship between geometry-induced heat accumulation and the resulting microstructures and mechanical properties. The thermal history was investigated by in situ process monitoring and multi-scale thermal analysis. The interlayer temperature at the top surface during the process varied significantly with the bipyramidal geometry, ranging from below 100°C to above 500°C. This interlayer temperature also affected melting and solidification on a microscopic time scale, thereby altering the melt-pool shape, cooling rate, and temperature gradient. Furthermore, the intertrack temperature increased near the pyramid apex because the heat deposited by adjacent laser tracks did not fully diffuse before the next scan pass occurred. Despite these pronounced variations in thermal history, the as-built sample showed only slight site-dependent variations in average grain size, KAM value, non-twin-related HAGB density, and hardness, which generally followed the geometry-dependent trends in thermal history.

An accurate prediction of the austenite-to-ferrite (γ → α) phase transformation using the multi-phase-field (MPF) model requires both the incorporation of thermodynamic calculations based on the CALPHAD method and the identification of model parameters. In this study, a Markov chain Monte Carlo (MCMC)-based parameter-estimation framework was developed to evaluate model parameters and their uncertainties using experimental data. To reduce the computational cost of the MPF simulation and enable parameter estimation within a reasonable computational time frame, neural-network surrogate models were constructed to perform thermodynamic calculations. By introducing surrogate models, the MPF simulation was accelerated by more than 220 times compared with conventional MPF simulations coupled with Thermo-Calc software. Subsequently, the developed framework was validated through numerical experiments in which we checked whether the framework can estimate ground-truth parameters using synthetic data obtained from an MPF simulation. The results demonstrated that the framework can accurately estimate the parameters and their uncertainties over a wide range of experimental uncertainties. Furthermore, the developed framework was applied to estimate the interfacial mobility and its uncertainty from the evolution of the α-phase volume fraction during the isothermal γ → α transformation in an Fe–0.19C–1.00Mn (wt.%) alloy. The estimated interfacial mobility parameter was of the same order of magnitude as values reported in previous studies, supporting its physical plausibility. Overall, this study contributes to the accurate prediction of microstructural evolution during the γ → α phase transformation by providing a framework for estimating the model parameters and quantifying their uncertainties based on experimental data.

To clarify the foaming behavior of FeO-containing slags during pulverized coal injection, calcined anthracite powder was introduced under continuous Ar gas blowing, and the temporal change in foam height was measured. CaO–SiO₂–FeO–Al₂O₃ and CaO–SiO₂–FeO–MgO slags were used. Relatively large bubbles were formed when only Ar gas was blown, whereas after pulverized coal injection, a film-like structure formed on the slag surface and the foam height increased markedly. For the Al₂O₃-containing slag, injection of 0.1 g of pulverized coal resulted in maximum foam heights of approximately 30 mm in the first injection and 65 mm in the second injection. SEM observation and EDS analysis revealed phases corresponding to wüstite, gehlenite, and fine metallic Fe in the upper region of the Al₂O₃-containing slag, and phases corresponding to wüstite and metallic Fe in the film-like sample from the MgO-containing slag. In foaming caused only by Ar gas blowing, the foam height increased on the higher-viscosity side, whereas during pulverized coal injection, the maximum foam height increased with increasing temperature. The MgO-containing slag showed a lower foam height than the Al₂O₃-containing slag under Ar gas blowing alone, but exhibited rapid and pronounced foaming during pulverized coal injection. These results suggest that foaming during pulverized coal injection is likely a multiphase reaction phenomenon governed by the combined effects of liquid-phase viscosity, gas generation through the carbonaceous material–FeO reaction, dispersion of solid phases or metallic Fe particles, and gas retention within the foam films.

In the iron-making process, wet granulation is a key process for utilizing dephosphorized fine ore powders as a raw material. However, dephosphorized ore powders with higher degree of reduction can result in a significant decrease in strength of the green pellets. Moreover, pellet-strength-enhancing effect by adding quicklime was less pronounced in reduced iron ore powder. Therefore, it is essential to investigate the underlying mechanisms that are responsible for the less binder efficiency of quicklime in reduced fine ore powders. To this end, this study investigated effect of quicklime addition on the compressive strength of green pellets prepared from magnetite and hematite. The results exhibited that the addition of quicklime to hematite can significantly enhance their green pellet strength, whereas the addition to magnetite resulted in no strength-enhancing effect on the pellet. The agitation torque of wet powder samples suggested that in the hematite the quicklime reacted well with added water, enhancing the plasticity of the wet powder. In contrast, in the magnetite the quicklime was unlikely to react with water, resulting in much less plasticity-enhancing effect. From several characterizations, wettability of the ore powder was considered to be a key property causing this contrasting response. A mechanistic scenario arising from hydration reaction of quicklime and subsequent formation of fine particles was proposed as a cause of the contrasting response. Finally, it was demonstrated that the green pellet strength can be significantly increased by using ground quicklime.

The effects of Al₂O₃ concentration and cooling rate on the crystallisation during cooling of SFCA-III were investigated using in-situ X-ray diffraction. Experiments were conducted at an oxygen partial pressure of 5 × 10^-3 atm in the range 298-1623 K and using synthetic iron ore sinter mixtures with basicity (CaO/SiO₂ ratio) of ~4. They showed that SFCA-III formed as the first phase to crystallize, from a high temperature phase assemblage comprising magnetite and melt, when the Al₂O₃ concentration in the mixture was at or above 0.33 mass%. At 0.22 mass% Al₂O₃, SFCA-III did form however β-CFF was the first phase to crystallize from the melt. At 0.09 mass% Al₂O₃, the key diagnostic in-situ XRD peak for SFCA-III was almost indistinguishable from the background X-ray intensity and, therefore, the lower limit of Al₂O₃ concentration where SFCA-III is observed to form during cooling at pO₂ = 5 × 10^-3 atm is close to 0.09 mass%. Cooling rate experiments showed that for the mixture with 1 mass% Al₂O₃, SFCA-III was preserved to 298 K when the cooling rate below 1433 K was at or above 17.5 K min^-1, after a regime of slower cooling at 2 K min^-1 in the range 1623-1433 K. Finally, in separate experiments involving change in pO₂ during cooling, we found tentative evidence that SFC-III does form in the Al₂O₃-free system, albeit within a narrow temperature range and with low abundance. These results further the understanding of the compositional and thermal factors that govern SFCA‑III formation during iron ore sintering.

Wear in slurry systems is strongly influenced by the combined action of erosion and corrosion, making it essential to understand how flow conditions and particle characteristics affect material degradation. This study investigates erosion–corrosion behavior using a rotational Taylor vortex device and develops a predictive model for estimating mass-loss rates. Experiments were conducted on SS400 steel using silica sand particles of fine, medium, and coarse sizes at concentrations of 0, 10, and 30 vol% over a range of Reynolds numbers. Under particle-free conditions, the mass-loss rate increased with Reynolds number due to enhanced corrosion. In contrast, under slurry conditions, the mass-loss response exhibited a non-linear trend, with a decrease observed at higher Reynolds numbers, indicating the presence of a corrosion-resistance effect. Based on the experimental mass-loss-rate trends, a predictive model was developed to estimate mass-loss rates by separating erosion-related and corrosion-related contributions, while implicitly accounting for their interaction through an empirical formulation. The model showed good agreement with experimental data across all test conditions. The proposed framework provides a practical method for evaluating erosion–corrosion behavior and quantifying the relative contributions of erosion and corrosion in vortex-driven slurry environments.

The microstructural dependence of hydrogen entry and permeation behaviors was investigated using SUS329J4L duplex stainless steel as a model material by correlative multimodal analysis combining scanning Kelvin probe force microscopy (SKPFM), SEM, EBSD, and EDS within the same observation area. Continuous SKPFM observations revealed surface potential changes associated with hydrogen entry predominantly in the ferrite phase on the hydrogen entry surface, consistent with its high hydrogen diffusivity. On the hydrogen permeation surface of the thinner specimen, surface potential changes associated with permeated hydrogen were also observed predominantly in the ferrite phase. In contrast, in the thicker specimen, distinct surface potential changes were observed in the vicinity of the ferrite–austenite phase boundaries. These results suggest that the layered microstructure and the low hydrogen diffusivity of the austenite phase restrict hydrogen transport through the ferrite phase over longer diffusion distances, possibly resulting in local hydrogen accumulation near the ferrite–austenite phase boundaries. Furthermore, the present study demonstrates that SKPFM-based correlative multimodal analysis is a useful approach for visualizing surface potential changes associated with hydrogen entry and permeation and for elucidating the relationship between hydrogen transport and microstructural features in duplex stainless steels.

During the process of electric arc furnace (EAF) steelmaking, the coherent jet plays a vital role in stirring and decarburization of the molten bath. Its flow field characteristics are influenced by the parameters of the shrouding gas. Improving the impact capability of coherent jets has been a hot research topic in recent years, with one method being the use of supersonic shrouding gas, known as supersonic combustion coherent jet technology. However, the mechanism by which a supersonic shrouding gas influences the main oxygen jet remains unclear. To investigate and quantify the effect of the shrouding gas parameters on the main oxygen jet, the flow fields of the SC coherent jet under different shrouding gas parameter conditions are investigated by both numerical simulation and combustion experiment. The results show that the potential core length of the main oxygen jet is negatively correlated with both the shrouding gas temperature and the distance between the shrouding gas and the main oxygen jet. The effect of the shrouding gas Mach number on the potential core length of the main oxygen jet shows a staged variation. Furthermore, a quantitative relationship between the potential core length of the SC coherent jet and the shrouding gas parameters is established.

To investigate the mechanism of steam injection on the sintering process under varying iron ore blending structures, this study conducted sinter pot experiments using two typical ore blends: one with a higher proportion of Australian limonite (Scheme 1) and the other with an increased proportion of Brazilian hematite (Scheme 2). Key injection parameters (duration, start time, flow rate, and pressure) were systematically optimized. The results show that steam injection significantly enhances sintering performance, with the optimal parameters being scheme-dependent. Under optimal conditions, Scheme 2 achieved a 12.1% increase in combustion speed, a 0.3% increase in yield, and a 4.5% increase in productivity compared to Scheme 1. Flue gas analysis revealed a distinct "low O₂, high CO₂, and high CO" pattern, indicating a shift from conventional solid-gas combustion to a more efficient gas–solid composite combustion mode triggered by the water–gas reaction. Mineralogical analysis further showed that Scheme 2 exhibited lower porosity and improved sinter strength. This study demonstrates that the effectiveness of steam injection is closely tied to the raw material structure, and the optimized synergy between steam parameters and ore blending provides a theoretical basis for precise "one-material-one-strategy" control in industrial sintering processes.

The use of biomass as an alternative reduction agent in the iron production process is an important concern in efforts to reduce dependence on fossil fuels and reduce CO₂ emissions. This study compares two approaches to biomass utilization, namely biomass pellets–iron ore and carbonized ore obtained through impregnation of biomass/coal tar into porous iron ore. Reductions were carried out on low-grade iron ore from Indonesia, which was characterized through the analysis of XRD, TGA/DSC, and the composition of the reaction gases. The results showed that the carbon in carbonized ore is better distributed in the pore structure, resulting in higher reduction efficiency at temperatures below 1000°C compared to the pellet method. The activation energy of the reduction reaction is also lower in carbonized ore, especially in the formation stage of iron metal (Fe). The addition of biomass of up to 15% to carbonized ore has been shown to be able to complete the reduction reaction completely and eliminate the wustite phase. The gas release characteristics of CO, CO₂, and H₂ show different stages of devolatilization and reduction between methods, with more controlled gas release in carbonized ore. Overall, the results show that the combination of carbonized ore and biomass additive methods provides superior reduction performance, making it a potential sustainable solution for the iron industry in the future.

The entry temperature of finish rolling is a critical process parameter in hot-strip production, particularly in endless rolling, where the high proportion of thin-gauge products makes rolling stability, energy consumption, and product performance highly sensitive to temperature non-uniformity. The DSCCR (Donghua Strip Continuous Casting and Rolling) process involves multi-stage coupling of heating, rolling, and reheating, while the periodic combustion reversal in regenerative furnaces further complicates temperature control. To address this issue, a temperature-field prediction framework combining a full-process two-dimensional transient heat-transfer model with parameter optimization was developed. A genetic algorithm was employed to calibrate correction coefficients for air cooling, furnace heating, and roll contact by minimizing the mean absolute error (MAE) across three key process stages.

Results indicate that optimization reduced the model's MAE and root-mean-square error (RMSE) from 7.506 °C to 4.534 °C and 8.967 °C to 6.504 °C, respectively. An independent holdout validation yielded an MAE of 4.486 °C and RMSE of 6.570 °C (reductions of 38.2% and 26.1% relative to the baseline). The close agreement between the optimization- and validation-set errors demonstrates that the calibrated coefficients maintain stable out-of-sample performance for an independent production batch of the same steel grade under similar operating conditions. Furthermore, the calibrated model quantitatively evaluated the effects of key process parameters and revealed the full-process thermal evolution mechanism. This physics-guided framework provides a reliable theoretical basis for precise temperature control, process optimization, and anomaly diagnosis in the endless rolling of ultra-thin strip steel.

This study investigated to optimize the Scanning Blue Laser-Enhanced Electrochemical Microscope (H-SBLEEM) for rapid, precise mapping of hydrogen migration rate distribution on iron, carbon steel, and welded carbon steel specimens. Under unmodulated laser irradiation, the laser irradiation response current (ΔI_H) increased proportionally with the hydrogen permeation current density (i_H) across different materials, validating ΔI_H as a reliable parameter to convert local hydrogen migration rate. With modulated laser light, a modulation frequency (f_mod) of approximately 0.5 Hz was determined as optimal, providing the ideal balance of a large laser irradiation response current amplitude (R) and minimal response time for high-speed imaging. Furthermore, R at 0.5 Hz maintained a proportional relationship with i_H. Applying H-SBLEEM to welded carbon steel allowed simultaneous measurement of the fused zone, heat-affected zone (HAZ), and base metal. Unmodulated laser irradiation induced that the softer base metal exhibited a larger ΔI_H than the harder fused zone and HAZ. Modulated laser irradiation provided that the time constant of decay curve in R coincided with that of i_H, with the softer base metal demonstrating earlier decrease in R than the harder welded zones.

Anode erosion during molten oxide electrolysis (MOE) remains a fundamental barrier to carbon-neutral ironmaking. In this paper, we demonstrate plasma MOE—in which a direct-current arc plasma serves as the anode to eliminate direct solid-electrode immersion in the melt—under high-temperature ironmaking conditions not previously explored, using an FeO–Al₂O₃ melt at ~1700 K under an argon atmosphere. Plasma MOE reduced solid-electrode erosion by one to two orders of magnitude relative to that obtained using immersed-electrode MOE (<0.01–0.05 mm² vs. 0.75–1.96 mm²). Polarity-reversal experiments revealed a polarity-dependent distribution of iron products, which cannot be explained by thermal reduction alone, suggesting an electrochemical contribution to iron formation. Iron formation observed during plasma MOE is comparable to that of immersed-electrode MOE, although a quantitative evaluation remains challenging. These results provide a proof-of-concept for plasma MOE as an approach that suppresses anode erosion while enabling iron production, indicating its potential as a promising route for carbon-neutral ironmaking.

When recycling scrap iron, impurities that are difficult to remove, called tramp elements, become a problem. Among them, tin (Sn) has many opportunities for contamination and affects the processability of steel; therefore, new removal methods are needed. Sn is highly reactive with iodine(I) and forms a metal iodide gas at high temperatures. The purpose of this was to remove Sn from iron scrap using I. We prepared carbon-saturated iron containing 2 mass% Sn as a sample, weighed 0.1 g, and placed it into the furnace. Subsequently, I₂ gas was injected introduced into the furnace. The Sn concentration and Sn removal rate were calculated by dissolving the sample after the experiment and performing an analysis using ICP-OES. Consequently, the Sn concentration in the sample was reduced to 0.008%, and the removal rate was up to 99.5%.

In can industry, film-laminated materials are being commercialized as environmentally friendly alternatives to painted ones. Polyethylene terephthalate (PET) film is widely used as a laminating material for steel sheets in beverage and food cans because of its excellent formability, corrosion resistance, and adhesion properties. In food cans, steam retort treatment is used for sterilization. However, the discoloration phenomenon, known as retort blushing, resulting from the exposure of the can's outer surface to water vapor, has emerged as a significant issue. To mitigate retort blushing, it has been found effective to use a film that blends polybutylene terephthalate (PBT), which crystallizes rapidly, with PET. This method increases the crystalline content in the film during steam retort processing, thereby enhancing its barrier properties against water vapor. Nevertheless, the effect of the crystalline state produced by this method on retort blushing remains unclear. Therefore, we investigated the influence of the PET film's crystalline state on retort blushing by subjecting the PET film laminated steel sheets to heat treatment, which were manufactured by changing the lamination temperature, and analyzing the crystalline structure using Raman spectroscopy. Our study revealed two key findings: (1) Simply changing the lamination conditions to control the oriented crystalline content does not completely prevent retort blushing, but applying heat treatment after lamination can fully suppress it. (2) Heat treatment induces isotropic crystal growth within the PET film near the interface with the steel sheet, which is believed to prevent the vaporization and expansion of moisture during the retort process, thereby preventing void formation and effectively mitigating retort blushing.

Low-grade Bayan Obo niobium concentrates are difficult to utilize because of their complex mineralogy, low niobium grade, and poor selectivity of conventional carbothermic processes. To address these challenges, a novel hydrogen reduction-stepwise smelting separation process based on a hydrogen-carbon coupled metallurgical concept was developed for the staged utilization of Fe-Nb-RE-Ti resources. The proposed process integrates selective hydrogen reduction, carbon-free melting separation, and carbothermic reduction through the intentional retention and inheritance of FeO between process stages. Hydrogen reduction at 800 °C produced direct reduced iron (DRI) with a metallization degree of 85.88%. Subsequent carbon-free melting separation at 1500 °C yielded metallic iron with a purity of 99.89 wt.% and generated a Nb-enriched primary slag without external flux addition. Carbothermic reduction of the primary slag at 1550 °C and a basicity of R=1.0 produced a FeNb alloy containing 11.19 wt.% Nb, while retaining RE and Ti in secondary slag. As a result, three value-added products, namely high-purity iron, FeNb alloy, and RE-enriched slag, were obtained through staged processing. Overall recoveries for Fe, Nb, RE, and Ti reached 96.26%, 87.18%, 96.76%, and 91.18%, respectively. Life-cycle assessment revealed that the process carbon footprint was 17.90 kg CO₂/kg alloy when green hydrogen was employed, representing a 53% reduction compared with the conventional route. The proposed process enables efficient stepwise separation and coordinated recovery of Fe, Nb, RE, and Ti from low-grade niobium concentrates, establishing a staged utilization pathway for this type of polymetallic resource and offering a novel green smelting approach for sustainable metallurgy.

9Cr ferritic/martensitic steel and 18Cr austenitic steel were exposed to steam (0.5 MPa), subcritical water (10.2 MPa), and supercritical water (22.7 MPa) at 650 °C for various durations. The pressure dependence of the oxidation rate constants of both steels was determined from the time dependence of specimen weight gain and oxide scale thickness due to oxidation. The oxidation rate constants of both steels decreased with increasing pressure. In steam, the oxidation rate constant of the 18Cr steel was smaller than that of the 9Cr steel. The difference in the oxidation rate constants between the two steels decreased with increasing pressure, and the oxidation rate constants became almost identical in supercritical water. The decrease in the oxidation rate constant with increasing pressure is considered to result from the reduction in voids in the formed oxide scales, which restricts the transport of metal and oxygen ions through the oxide scales.

The growing adoption of electric vehicles (EVs) places increasing demands on lithium-ion batteries (LIBs) to deliver both higher electrochemical performance and reliable safety under abnormal conditions. For prismatic LIBs used in EV applications, aluminum alloys are commonly employed as cell case materials; however, their relatively low melting point raises concerns during thermal runaway. Consequently, Ni-coated steel sheets have been investigated as alternative materials because of their higher melting point and superior mechanical strength. In recent prismatic battery designs, laser welding has been increasingly adopted; however, partial melting of the Ni coating within the weld zone may affect corrosion behavior in the battery electrolyte. In this study, the corrosion behavior of laser-weld zones in Ni-coated steel sheets was examined in LIB electrolytes. Localized electrochemical measurements and long-term immersion tests were conducted in a standard electrolyte and in an electrolyte containing 300 ppm water. The dissolution behavior of Fe ions was evaluated, and the influence of dissolved Fe ions on battery performance was investigated using lithium-ion cells fabricated with Fe-ion-containing electrolytes. Although the weld zones showed slightly higher initial Fe dissolution than the non-welded zones, no clear increase was observed with extended immersion time under the tested conditions. Moreover, no noticeable difference in capacity retention was observed over 40 charge–discharge cycles. These results suggest that, within the experimental conditions of this study, the corrosion behavior of laser-weld zones is comparable to that of non-welded zones.

This study investigates the effects of austempering temperature on the microstructure, mechanical properties, and wear behavior of Cu-Ni-alloyed austempered ductile iron (ADI). Microstructural characterization using optical microscopy (OM) and scanning electron microscopy (SEM) reveals that decreasing the austempering temperature refines the ausferritic matrix, which consists of acicular ferrite and carbon-enriched austenite. The specimen austempered at 260 °C exhibited the highest ultimate tensile strength and Brinell hardness, reaching 1440 MPa and 470 HB, respectively, while its elongation was 1.5%. These results reflect the high-strength, high-hardness, and low-ductility characteristics associated with low-temperature austempering. Wear resistance increased with decreasing austempering temperature and reached its maximum at 260 °C. This superior wear resistance is attributed to the combined effects of the refined ausferritic microstructure, graphite nodules, and protective oxide layers formed during sliding. Combined analysis of wear loss, friction coefficient, three-dimensional surface topography, two-dimensional depth profiles, and worn-surface morphology confirms the highest wear resistance at 260 °C and indicates abrasive wear as the dominant wear mechanism.

For the high-performance development of sliding parts, the tribological properties of carbon steel must be improved. In particular, adhesion is an important factor for controlling the tribological properties. However, the dependence of adhesion on crystal orientation has barely been investigated owing to the difficulty in obtaining a single crystal of steel. In this paper, a new analysis method combining electron backscatter diffraction and atomic force microscopy reveals the dependence of adhesion on crystal orientation in carbon steel. The adhesion force was found to increase in the order (100) < (111) < (110). In addition, molecular dynamics simulations can reproduce this trend and clarify the factors governing the dependence of adhesion on crystal orientation at the atomic level. The findings of this study can contribute to controlling the tribological properties of carbon steel and understanding the nanoscale phenomenon of mechanical contact.

The effect of Al content on the slag/steel reaction between quenching and partitioning (Q&P) steel with refining slag was investigated at 1873 K in a vertical Si-Mo heated furnace. The results shows that the chemical compositions of the steel and slag changed significantly as the Al content in steel increased. After the reaction between slag and steel, the Al content in the steel and the SiO₂ in slag increased for the experiment with 0.03% Al content. While in the experiment with high Al content (0.2% ,0.8% and 1.5% Al), Al content in steel and SiO₂ content in slag decreased. Thermodynamic analysis revealed that the main reducing agent was Si in the slag/steel reaction for the 0.03% Al steel, whereas it changed to Al for the steel contain 0.2% to 1.5% Al, which resulted in the opposite trend of the slag and steel compositions. In all experiment, the Mg content increased with increasing Al content. The characteristics of inclusions also evolved significantly with increasing initial Al content. In the experiment with Al content of 0.03%, 0.2%, 0.8%, the initial inclusions are mainly MnS. The inclusion changed into MgO and CaO-MgO-Al₂O₃ after the slag/steel reaction. For the experiment with 1.5% Al, the initial inclusions are mainly AlN and MnS, and it changed into CaO-MgO-Al₂O₃ after the slag/steel reaction. The variations in Al content exerted a significant influence on the reaction between the Q&P steel and refining slag.

The Fe–10%Mn–0.1%C alloy exhibits an ultra-fine microstructure containing α'-martensite (bcc), ε-martensite (hcp), and retained austenite (fcc). However, Mn causes grain boundary embrittlement and intergranular fracture at prior austenite grain boundaries at low temperatures. In this study, <0.9 mass% Mo was added to Fe–10%Mn–0.1%C alloys to suppress intergranular fracture and improve their toughness in their as-quenched states. Electron backscatter and neutron diffraction revealed that Mo addition displayed little influence on the prior austenite grain size, martensitic block width, and phase fractions. Scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy indicated that Mo segregated at the prior austenite grain boundaries at approximately 3 mass% after austenitizing 0.9%Mo steel at 1173 K, whereas Mn segregation remained almost unchanged. Thermodynamic calculations using the Hillert–Ohtani model confirmed that Mo exhibited a stronger segregation tendency than that of Mn. Charpy impact tests indicated that the ductile-to-brittle transition temperature (DBTT) decreased from 275 K for the Mo-free steel to 220 K for the 0.9%Mo steel. Fractographic observations revealed that intergranular fracture, which was dominant in the Mo-free steel at 77 K, was significantly suppressed by Mo addition. In the 0.9%Mo steel, intragranular fracture occurred with a characteristic size corresponding to the block size of α'-martensite. Therefore, Mo segregation effectively strengthens the prior austenite grain boundaries and suppresses intergranular fracture within Fe–10%Mn–0.1%C steel, leading to an improved low-temperature toughness and a reduced DBTT.

To improve the fatigue strength of austenitic stainless steel without compromising its corrosion resistance, fine particle peening (FPP) with chromium particles was applied to 316L steel. The microstructural characteristics, fatigue properties, and corrosion behaviors of the treated steel were investigated and compared with those of specimens subjected to conventional peening with steel particles. The fatigue strength of the steel treated by FPP with chromium particles was higher than that of the specimen treated by peening with large steel particles, because smaller surface dents were formed. However, it was lower than that of the specimen treated by FPP with steel particles owing to the lower surface hardness and compressive residual stress. The corrosion resistance of the steel treated by FPP with chromium particles was comparable to that of the polished specimen and superior to that of the specimens treated by peening using steel particles. This improvement was attributed to the suppressions of steel particle transfer and deterioration of the surface morphology. To further enhance the fatigue strength, a mixture of fine steel and chromium particles was mechanically milled to produce fine steel particles coated with a chromium layer. FPP with these mechanically milled particles resulted in a higher fatigue strength than FPP with chromium particles because of the increased surface hardness and compressive residual stress. However, its corrosion resistance was the lowest among all the specimens tested, possibly because the transferred chromium detached during the immersion test.

In ultra-high cleanliness steel, it is necessary to control not only primary inclusions but also fine secondary inclusions generated during solidification process. Therefore, thermodynamic information on molten steel and inclusions at solidification temperatures is required to establish precise inclusion control. However, past thermodynamic studies of molten steel and oxides have been conducted mainly around the steelmaking temperature of approximately 1873 K, and there have been no studies below 1773 K. In this study, equilibrium experiments between Fe-Ni alloy and Al₂O₃-MnO-SiO₂ slag were conducted. Fe-Ni alloys are used in precision machinery and microfabrication due to their low thermal expansion. Al₂O₃-MnO-SiO₂ system is one of the major composition of inclusions of Fe-Ni alloys. By using an Al₂O₃ crucible in equilibrium experiments, Al₂O₃ saturation condition (activity of Al₂O₃ is unity) was achieved, and the Al deoxidation equilibrium of Fe-36mass%Ni and Fe-50mass%Ni was measured. The experimental temperature was set at 1733K, which is near the solidification temperature of Fe-Ni alloys. This is the lowest temperature studied on Al deoxidation equilibrium of Fe-Ni alloys. The experimental results were analyzed based on Wagner's interaction formalism. Then interaction coefficients for the Al deoxidation equilibrium of Fe-Ni alloys valid from 1733 K to 1973 K were determined. Liquid Al₂O₃-MnO-SiO₂ slag compositions saturated with Al₂O₃ were also obtained in this study, and the reported phase diagrams of Al₂O₃-MnO-SiO₂ system were also evaluated.

Low-alloy wear-resistant steels with different lanthanum additions (0, 25, 40, 96, 320, 620, 1500, and 4800 ppm) were prepared to investigate effects of La content on abrasive wear behavior, hardness, inclusion characteristics, and wear mechanisms. After forging at 1200 °C and quenching at 890 °C, the wear resistance and microstructural evolution of the steel were systematically investigated. With increasing La content, the mass loss, surface roughness, and thickness of the plastically deformed layer initially decreased and then increased, reaching optimal values at 320 ppm La. The steel with 320 ppm La exhibited a 22% reduction in mass loss, a 48.7% decrease in surface roughness, and the highest hardness of 48.6 HRC, effectively suppressing abrasive groove formation.

First-principles calculations were used to determine the elastic constants and theoretical hardness of inclusion phases. Combined with experimental characterization of worn surfaces and subsurface structures, the role of inclusion hardness in wear resistance was clarified. Relatively hard inclusions, including LaAlO₃, CaS, LaP, and LaAs, enhanced resistance to abrasive ploughing, whereas soft inclusions such as CaAl₄O₇ and La₂O₃ acted as preferential damage sites. The maximum number density of relatively hard inclusion phases reached 124.56 #/mm² at 320 ppm La. Under wet rubber wheel abrasion with a load of 100 N, severe grooving dominated the wear process, and wear resistance was governed by both matrix hardness and relatively hard inclusion phases. An inclusion-related hardness contribution factor, H, was proposed to quantify the effect of inclusions. Excessive La addition promoted coarse C-bearing inclusions and deteriorated wear resistance.

The utility of hyperspectral measurement was assessed as a means of predicting the corrosion risk of steel materials based on surface information. Carbon steels exposed to outdoor conditions in Choshi and Miyakojima were used as the test specimens. Exposure tests were conducted every six months for a duration of two and a half years. Corrosion loss was calculated by comparing the weight of specimens before exposure tests and after removing corrosion products from the surface. Hyperspectral measurements were conducted on these specimens, with corrosion products identified through SAM (Spectral Angle Mapper) analysis. α-FeOOH, β-FeOOH, γ-FeOOH, and Fe₃O₄ were employed as reference data for SAM analysis. In both Choshi and Miyakojima test sites, γ-FeOOH was predominantly detected on the specimens after ordinary exposure tests, whereas Fe₃O₄ was prevalent on the specimens exposed to sheltered environments. The correlation between the proportion of each corrosion product identified through SAM analysis and the amount of corrosion change over one year was investigated. α-FeOOH showed a positive correlation with the amount of corrosion change, whereas the amount of corrosion change tended to decrease with an increase in the β-FeOOH fraction.

In thermal desorption spectroscopy (TDS) tests, temperature changes during the test, which in turn causes changes in trap sites such as dislocations and precipitates. To take this into account, a novel model of hydrogen diffusion is proposed. To consider the hydrogen diffusion, TDS tests at a heating rate of 100^oC/h were conducted using SUS310S stainless steel and A6056 aluminum alloy. The temperature range for TDS testing was from room temperature to 800°C for SUS310S and from room temperature to 500°C for A6056. Before the TDS tests, the SUS310S specimen was charged with hydrogen by keeping it in pure hydrogen gas at 200^oC and 10MPa, while the A6056 specimen was charged with hydrogen by an electrochemical method. It is shown that the TDS curve numerically calculated using the diffusion coefficient depending on temperature that follows a single straight line on an Arrhenius plot can explain the experimental result of SUS310S fairly well, while they could not reproduce the experimental data of A6056 because the TDS test result of A6056 exhibited the tendencies that the hydrogen release rate below 430^oC was very low and that the release rate abruptly increased around 430^oC. The TDS curve numerically calculated using the diffusion coefficient based on the novel model proposed in this work can reproduce the experimental data of A6056 fairly well.

Carbon dioxide, a well-known greenhouse gas, has significantly contributed to global warming. However, during the steelmaking and refining processes, it was also a kind of oxidizing agent at temperatures ranging from 1450 to 1650 °C. In this research, a series of high-temperature experiments, water experiments, and numerical simulations have been conducted to assess the feasibility of the CO₂ bottom-blowing mode in the 120t LF (ladle refining furnace) process. The results of laboratory research indicated that the reaction rate of CO₂ was 8.9 %, when the [C] content and temperature of the molten bath were 0.130 mass% and 1550 °C, respectively. When the CO₂ bottom-blowing mode was employed, although it caused an uneven distribution of [C] in the molten bath, the mixing time was reduced by 8.2%, and the average velocity of the molten bath increased by 10.0%, compared to the Ar bottom-blowing mode.

A parametric analysis using a three-dimensional Eulerian multiphase model evaluated interfacial force effects on mass flow rate in an RH reactor. Twenty-two scenarios were analyzed, considering four drag models (Schiller-Naumann, Ishii-Zuber, Tomiyama, Symmetric), Simonin turbulent dispersion (C_TD = 0.0, 0.45, 0.55, 0.75), virtual mass (C_VM = 0.0, 0.25, 0.45, 0.75), and Sato turbulent interaction (BIT = 0.0, 0.05, 0.2, 0.6). The Ishii-Zuber model showed discrepancies up to 12.1% versus Schiller-Naumann, while Tomiyama exhibited closest agreement (≈1.5%). Turbulent dispersion was most influential; its omission reduced mass flow by 70%–83% across all drag models. Virtual mass demonstrated nonlinear behavior strongly dependent on drag selection: intermediate coefficients (C_VM = 0.45) reduced recirculation up to 10%, while extreme values (C_VM = 0.25 or 0.75) produced moderate increases up to 7%. Notably, Ishii-Zuber proved considerably more sensitive to virtual mass variations than Schiller-Naumann. Turbulent interaction effects varied markedly between drag models, exhibiting progressive or non-monotonic responses. Crucially, turbulent dispersion calibration proved inseparable from submodel coupling—reducing C_TD occasionally increased mass flow, highlighting interfacial force interdependence. The configuration combining Schiller-Naumann drag, Simonin turbulent dispersion (C_TD = 0.55 or C_TD = 0.75), Sato turbulent interaction (BIT = 0.2), and virtual mass (C_VM = 0.75) yielded recirculation values consistent with experimental data. ANOVA confirmed turbulent dispersion and virtual mass primarily controlled recirculation, while drag model lacked statistical significance. These findings demonstrate literature discrepancies stem from interfacial sub-model coupling rather than individual drag selection.

To clarify the brittle fracture mechanism in a Charpy impact test of pearlitic steel, the fracture surface and microstructure near the crack initiation were observed. The results indicate that plastic deformation in a pearlite block influences crack initiation (shear cracking). Furthermore, a fracture model in which macroscopic brittle failure occurs through the following failure processes was proposed: (1) slip deformation in the block, (2) shear cracking, (3) cracking along the slip plane, and (4) cleavage fracture. In this model, the fracture mode transitions from a shear-dominated mode to an opening-dominated mode from crack initiation to macroscopic failure.

The thermal decomposition of CaCO₃ in air is often simulated using the shrinking core model. In high temperature molten slag, however, mass transfer of product gas is caused by the pressure-driven flow in the product layer, which is not considered in conventional shrinking core models. In this study, a pressure-based shrinking core model (PSCM) was proposed to consider this pressure-driven gas flow. The model simultaneously incorporates heat and mass transfer in the CaCO₃ particle, as well as the interfacial reaction, and is therefore applicable regardless of the rate-limiting step. The PSCM simulation results were compared with one-dimensional model (ODM) simulations and experimental data reported in the literature. The comparison results demonstrated that the PSCM accurately predicts the decomposition degree, reaction interface temperature and pressure in the particle as long as the assumption of a shrinking core formation remains valid. The PSCM and the ODM results indicated that both heat and mass transfer play significant roles in the thermal decomposition of CaCO₃. During the reaction, the interface temperature remained below the slag temperature due to the strong endothermic reaction and heat transfer limitation in the product layer. Meanwhile, the interface pressure increased monotonically because of CO₂ generation and accumulation at the reaction interface with mass transfer limitation in the product layer.

Titanium-bearing blast furnace slag (Ti-bearing BF slag) is a major industrial by-product generated during the blast furnace smelting of vanadium–titanium iron concentrate. More than 50% of the titanium resources in vanadium–titanium magnetite are transferred into the slag phase during smelting, making Ti-bearing BF slag an important secondary titanium resource. However, titanium components in Ti-bearing BF slag are highly dispersed in multiple Ti-rich mineral phases, such as perovskite, titanaugite, titanium-rich diopside, titanium carbonitride, and magnesium–aluminum spinel. These phases generally have fine particle sizes, commonly less than 10 μm, and similar surface physicochemical properties, making efficient separation by conventional beneficiation methods extremely difficult. Consequently, large quantities of Ti-bearing BF slag have long been stockpiled, resulting in serious titanium resource loss and substantial land occupation. In this review, current technologies for the comprehensive utilization of Ti-bearing BF slag are systematically summarized and classified into non-titanium-extraction and titanium-extraction routes. The latter mainly include acid/alkali leaching, thermal reduction, high-temperature carbonization followed by low-temperature chlorination, and mineral phase reconstruction coupled with beneficiation separation. Particular attention is paid to the technical limitations and future challenges of these processes, including high reagent and energy consumption, secondary pollution, low separation efficiency, and limited industrial feasibility. Based on a comparative analysis of different titanium-extraction routes, mineral phase reconstruction coupled with beneficiation separation is identified as a promising and relatively feasible strategy. Furthermore, selection criteria for suitable Ti-rich phases are proposed, providing guidance for the design of efficient titanium recovery processes from Ti-bearing BF slag.

Finite element method (FEM) simulations were conducted to evaluate the crash performance of 1500 MPa-grade ultra-high-strength steel (UHSS) for lightweight automotive structures. To investigate the effect of ductility, three-point bending tests were performed on 1500 MPa-grade steel sheets with varying elongation properties. FEM simulations were then carried out to assess the ability of the Swift-type constitutive model to reproduce experimentally observed crash behavior. However, the model could not capture the improvement in crashworthiness associated with increased elongation. In contrast, FEM simulations using experimentally measured stress–strain curves successfully reproduced this effect.

Comparison between the experimental stress–strain curves and those predicted by the Swift model revealed that the model does not account for the gradual transition from elastic to plastic deformation observed in real materials.

To reproduce this transition behavior, a new constitutive model was proposed that considers micro-yielding behavior and the Schmid factor to represent the progressive onset of plasticity. This model showed improved agreement with experimental results, accurately reproducing both the work-hardening behavior and the influence of elongation on crash performance.

These results indicate that crash performance is strongly influenced by work-hardening behavior during the transition from elastic to plastic deformation, rather than by elongation itself, and that accurate representation of this behavior is essential for crash simulations of 1500 MPa-grade steels.

For the sake of the recycle of waste PVC in the process of ferronickel production, reaction behaviors of mixtures of Fe₂O₃ and PVC, and NiO and PVC were investigated at elevated temperatures from 623K(350^oC) to 1273K(1000^oC) under Ar atmosphere. The obtained reaction products were examined using XRD and thermodynamic considerations were carried out. The explanations of reaction mechanism through thermodynamic consideration were excellent agreement with experimental results.

HCl evolution occurred from 523K(250^oC) to 650K(377^oC) which was almost the same as the literature value. Reaction products of mixtures of Fe₂O₃ and PVC, and NiO and PVC at 623K(350 ^oC) showed an existence of FeCl₂ and NiCl₂ respectively. When temperature increased, Fe₂O₃ reduced to Fe₃O₄ from 723K(450^oC) to 873K(600 ^oC) and completely reduced to Fe at 1073K(800^oC) and 1273K(1000^oC). The mixture of NiO and PVC showed a mixture of NiO-NiCl₂-Ni at 723K(450^oC), and reduced to Ni completely at 923K(650^oC). These reduction behaviors occurred very low temperature in comparison with ordinary reduction system such as CO or H₂ reduction. It was considered that a chlorination reaction in low temperature at 623K(350^oC) will affect to the later reduction behavior in higher temperature.

This paper presents a mathematical analysis of diffusion and interfacial reaction in a single slit pore of an iron ore pellet under H₂/CO atmospheres. The slit pore is used as a simplified microstructural model to examine how local pore geometry influences mass transfer and reaction conditions during reduction. Three slit-pore cross-sectional shapes are considered: triangular, parabolic concave, and parabolic convex. The results show that slit-pore geometry affects local mass transfer efficiency and changes the relative influence of diffusion and chemical reaction. The analysis also indicates that narrow and deep slit pores are more sensitive to diffusion limitations, particularly in hydrogen-rich atmospheres, which may contribute to the development of crack-like features during reduction. Model trends were consistent with published experimental and calculated observations.

During the production of grain-oriented silicon steel in wide hot strip mills, the operating side (OS) of the strip is highly prone to unilateral quarter-wave defects due to its specific production process and the high deformation resistance of the material. Currently, wide hot strip mills are generally equipped with Continuously Variable Crown (CVC) roll contours. However, owing to the symmetrical design of CVC contours, it is difficult to effectively regulate unilateral local profile features. To address this issue, this paper proposes an Asymmetric Heteromorphic Roll (AHR) contour based on the local curve superposition method. This scheme adopts a configuration strategy combining local cosine compensation on the OS of the top work roll with a standard CVC contour on the bottom work roll, aiming to control the unilateral quarter-wave in grain-oriented silicon steel. Numerical calculations and simulation analyses indicate that this roll configuration can effectively optimize the inter-roll contact pressure distribution and improve the cross-sectional profile of the finished strip. Furthermore, the control effect on the OS quarter-wave of grain-oriented silicon steel was verified on a 2250 mm hot strip mill production line. Industrial trial results demonstrate that this roll configuration significantly reduces the incidence of quarter-wave defects on the OS while maintaining the original quadratic crown adjustment capability.

The degradation and sticking behavior of iron ore pellets during reduction are critical factors affecting the stability of hydrogen-based ironmaking processes. In this study, these phenomena were experimentally evaluated from a mechanical perspective using three types of pellets with different basicity. The compressive strength of the pellets was measured at room temperature, and the statistical distribution was analyzed using a Weibull approach. The results showed that fracture behavior varied depending on pellet type, with the high-basicity pellet exhibiting multiple fracture modes and the acidic pellet showing larger variability in strength. High-temperature reduction and tensile tests were conducted continuously under controlled load conditions without interrupting the reduction atmosphere. This experimental approach enables direct evaluation of inter-particle adhesion formed during reduction. All pellets exhibited characteristic expansion followed by shrinkage, with the acidic pellet showing the largest deformation. The tensile test performed under reduction conditions revealed that the acidic pellet exhibited the highest tensile stress, indicating strong inter-particle adhesion. A relationship between degradation and sticking was observed. Pellets with lower compressive strength tended to undergo larger deformation, which can lead to increased contact area and enhanced sticking. The observed relationship depends on the evaluation parameter, with adhesion force showing a clearer trend than tensile stress. These findings demonstrate that both mechanical strength and deformation behavior govern sticking behavior, and highlight the importance of direct mechanical evaluation under reduction conditions for assessing pellet performance.

Overcoming delayed fracture under atmospheric corrosion environment is a critical challenge for the practical application of ultra-high-strength bolts. This study investigated the delayed fracture behavior of 1700 MPa-class quenched and tempered bolts fabricated from a 0.4%C-2%Si-1%Cr-1%Mo steel (mass%) by means of outdoor exposure tests, accelerated tests, and thermal desorption spectrometry. In a 10-year outdoor exposure test, the delayed fracture behavior of the ultra-high-strength bolts was categorized into two types: rupture at the thread runout and the first thread root in nut, and fracture at the thread root in nut and the under-head fillet. Outdoor exposure tests using notched bolts could reproduce the delayed fracture at the thread runout. By measuring the strain change for the shank of notched bolt during the outdoor exposure test, we successfully observed the delayed fracture process: the initiation of intergranular fracture along the boundaries of prior-austenite grains, followed by unstable fracture, and culminating in the formation of a shear lip. The delayed fracture of the bolts was attributed to hydrogen embrittlement. Slow-strain-rate testing for hydrogen-pre-charged notched specimens showed a linear relationship between the fraction of intergranular fracture (IGF) area and the peak value of the maximum principal stress σ_max* at the notch root. The delayed fracture mechanism of the ultra-high-strength bolts was discussed based on the σ_max* and the IGF area fraction at the fracture locations.

The effects of metal cations on corrosion and hydrogen absorption behavior of iron and steel were investigated in NaCl, MgCl₂, and ZnCl₂ solutions using a laser local activation method. Electrochemical hydrogen permeation measurement was performed, combined with surface characterization and analysis. The results reveal that metal cations significantly affect the corrosion and hydrogen permeation behavior of steel and iron in chloride-containing solutions under localized laser activation conditions. Zn²⁺ led to a higher amount of diffused hydrogen through iron and steel compared to Na⁺ and Mg²⁺. The surface analysis demonstrated the formation of a protective Zn-containing film on the iron and steel surfaces. However, once this protective film is damaged by laser irradiation, a localized activation region is formed for the cathodic hydrogen evolution reaction, resulting in a more significant hydrogen entry into iron and steel compared to NaCl and MgCl₂ solution environments.

The changes in the apparent hydrogen diffusion coefficient of high-strength steel subjected to repeated cycles of hydrogen charging under strain and subsequent unloading were investigated using JIS-SCM435 steel. The objective of this study was to clarify whether the application of cyclic strain during hydrogen charging promotes the formation of lattice defects that act as hydrogen traps, and whether such defects can be detected by evaluating the apparent hydrogen diffusion coefficient obtained from hydrogen permeation tests.

The results showed that the apparent hydrogen diffusion coefficient increased with the application of strain, while it decreased with an increasing number of cyclic strain cycles applied under hydrogen charging. Notably, the apparent hydrogen diffusion coefficient did not decrease monotonically with increasing cyclic strain up to fracture. Furthermore, the difference in the apparent hydrogen diffusion coefficient between the unstrained condition and the condition prior to fracture was quantitatively evaluated. It is suggested that this decrease in the apparent hydrogen diffusion coefficient represents a candidate threshold material parameter that can be used to predict hydrogen embrittlement.

In the electrochemical hydrogen penetration test using the Devanathan-Stachurski cell, the hydrogen penetration of metal thin films consists of multiple processes: hydrogen evolution, hydrogen entry and hydrogen diffusion. The admittance of the iron electrode was theoretically derived when the hydrogen evolution reaction consists of the Volmer and Heyrovsky reactions in acidic solution and hydrogen entry into iron electrode occurs. Under the same conditions, a new transfer function, penetration admittance, was derived. The penetration admittance is the ratio of the alternating potential modulation of the hydrogen entry surface and the alternating current response of the hydrogen detection surface. Assuming that hydrogen diffusion in metal films obeys Fick's second law, we derived the theoretical formula of complex penetration ratio, which is the ratio of hydrogen entry and hydrogen detection in the frequency domain. By dividing the penetration admittance by the complex penetration ratio, we derived a second new transfer function "entry admittance" which is related to time constant of hydrogen adsorption/desorption on metal. Furthermore, by comparing the admittance and the entry admittance, we theoretically showed that the ratio of the rate constants of the hydrogen evolution reaction and the hydrogen entry reaction can be obtained.

Ammonium thiocyanate (NH₄SCN) is widely used as a promoter for hydrogen entry in electrochemical hydrogen charging. However, the consumption of thiocyanate ions (SCN⁻) due to electrode reactions at the Pt counter electrode may influence the stability and reliability of electrochemical hydrogen permeation measurements. In the present study, the electrode reactions at the Pt counter electrode during electrochemical hydrogen charging were investigated through electrochemical impedance measurements and Faradaic impedance simulations. The electrode potential of the Pt counter electrode was measured during cathodic polarization of a pure iron working electrode, and anodic polarization and impedance measurements were subsequently performed using a Pt working electrode. Three-dimensional complex impedance plot analysis revealed that the instantaneous impedance in the NH₄SCN-containing solution comprises a capacitive loop in the high-frequency region and an additional low-frequency feature. The high-frequency loop varied with applied potential, indicating its association with the electrode/solution interface, whereas the low-frequency feature exhibited minimal potential dependence and was attributed to Faradaic processes associated with SCN⁻ oxidation. The impedance response was reproduced by Faradaic impedance simulations based on a reaction model involving SCN⁻ adsorption and subsequent decomposition. Collectively, these results suggest that the proposed model adequately describes the key electrochemical processes occurring at the Pt counter electrode.

Steel products used in atmospheric environments are susceptible to corrosion as aqueous aerosols bring moisture into contact with the steel surface. The atmospheric (cyclic wet-dry) corrosion plays an important role in the hydrogen generation. Therefore, the simultaneous measurement of hydrogen permeation current, and hydrogen entry side potential and pH during cyclic wet-dry corrosion tests is required. The combination of an all-solid-state reference electrode and W electrode were applied to detect hydrogen entry side potential and pH. The optimized configuration of the sensing electrodes make it possible to measure the potential and pH without hinder hydrogen permeation current.

Using Scanning Blue Laser-Enhanced Electrochemical Microscope for Hydrogen detection, detailed visualization of hydrogen migration rate distribution on an annealed iron plate specimen was attempted. To visualize the distribution, a blue laser was irradiated and scanned on the hydrogen detection surface of the specimen during the electrochemical hydrogen permeation test, and a laser irradiation response current (convertible to hydrogen migration rate) was measured. The scan was conducted around grain boundaries. As a result, when a cathode current density of -67 A·m^-2 was applied to the hydrogen absorption surface, unlike in previous reports, no influence of grain boundaries was observed on the hydrogen migration rate distribution. It was suggested that the distribution independent of grain boundaries was due to fluctuation in the hydrogen permeation current caused by repeated accumulation and removal of hydrogen bubbles on the hydrogen absorption surface during laser scanning. To suppress current fluctuations, the laser scanning distance was limited to the vicinity of the grain boundaries, thereby shortening the laser scanning time. The condition provided the hydrogen migration rate distribution showing the smaller rates around grain boundaries compared to inside grains. Furthermore, the rate at grain boundaries increased linearly with increasing steady hydrogen permeation rates, and then estimated to be approximately 1/4 of that inside grains.

Hydrogen diffusion and trapping in ultralow-carbon Fe, P-added Fe, S-added Fe, and SCM435 steel were investigated by electrochemical hydrogen permeation tests and thermal desorption analysis. The microstructures of the Fe-based specimens were varied by cold rolling, high-pressure torsion (HPT) processing, and subsequent heat treatment to clarify the effects of dislocations, grain boundaries, and solute-related lattice-defect states. The apparent diffusion coefficient, D_app, of non-deformed Fe was approximately 1.1×10^-8 m² s^-1 and showed little dependence on hydrogen concentration, C_H. In contrast, D_app markedly decreased in cold-rolled and HPT-processed Fe specimens, and their decay transients deviated from theoretical curves based on concentration-independent Fickian diffusion. In specimens containing a high density of lattice defects, D_app increased with increasing C_H, indicating apparent concentration-dependent diffusion associated with hydrogen trapping at lattice defects. Thermal desorption profiles showed that the absorbed hydrogen was mainly diffusible hydrogen trapped at relatively weak sites below approximately 200°C, with broad trapping states in the HPT-processed specimens. Fe(P) and Fe(S) showed trends similar to Fe, and no clear change in D_app attributable specifically to P or S addition was detected under the present experimental conditions. The reduction in D_app was therefore governed mainly by lattice-defect states introduced by deformation and modified by subsequent heat treatment. SCM435 exhibited D_app values comparable to dislocation-rich Fe, but its behavior reflected heterogeneous microstructural trapping states. Analysis based on the chemical diffusion coefficient derived from the Svoboda–Fischer framework indicated that dislocation-related traps reduce D_app in cold-rolled Fe, whereas grain-boundary-related traps dominate in ultrafine-grained HPT-processed Fe.

Creep testing is time-consuming and costly, leading institutions to limit the number of tests conducted to the minimum necessary for their specific objectives. By pooling data from each institution, it is anticipated that predictive models can be developed for a wide range of materials, including welded joints and degraded materials exposed to service conditions. However, the data obtained by each institution is often highly confidential, making it challenging to share with others. Federated learning, a type of privacy-preserving computation technology, allows for learning while keeping data confidential. Utilizing this approach, it is possible to develop creep life prediction models by leveraging data from various institutions. In this paper, we constructed global deep neural network models for predicting the creep rupture life of heat-resistant ferritic steels in collaboration with eight institutions using the federated learning system we developed for this purpose. Each institution built a local model using only its own data for comparison. While these local models demonstrated good predictive accuracy for their respective datasets, their predictive performance declined when applied to data from other institutions. In contrast, the global model constructed using federated learning showed reasonably good predictive performance across all institutions. The distance between each institution's data was defined in the space of explanatory variables, with the NIMS data, which had the largest dataset, serving as the reference point. The global model maintained high predictive accuracy regardless of the distance from the NIMS data, whereas the predictive accuracy of the NIMS local model significantly decreased as the distance increased.

This review summarizes representative studies on numerical simulations of ironmaking processes published between 2023 and early 2026, with emphasis on recent methodological developments, target phenomena, and engineering applications. It covers the major modeling frameworks used in ironmaking, including continuum multifluid models; computational fluid dynamics-discrete element method (CFD-DEM); interface-resolving methods, such as the volume of fluid method (VOF); mesh-free approaches, such as smoothed particle hydrodynamics (SPH); and hybrid- or data driven models, for prediction, monitoring, and optimization. This review is structured around distinct reactor regions and their underlying process phenomena, including burden distribution and gas–solid interaction in the shaft, raceway dynamics, softening–melting behavior in the cohesive zone, liquid flow in the dripping zone and hearth, low-carbon operational dynamics, and modeling of hydrogen based direct reduced iron shaft furnaces. The literature indicates that recent studies have shifted from simplified reactor scale descriptions to increasingly detailed multiscale and multiphysics representations. Moreover, the focus of the studies is also shifting from mechanistic interpretation to predictive and design-oriented simulation, supported by high-performance computing, surrogate-assisted modeling, and digital twin-oriented frameworks. Overall, recent progress in ironmaking processes suggests that numerical simulation is becoming an essential design and decision-support tool not only for conventional blast furnace analysis but also for developing low-carbon, hydrogen-based, and electrified ironmaking systems.

The yield in the iron ore sintering process is managed in daily operations as an important indicator of manufacturing costs and CO2 emissions. Currently, general yield operation actions are "feedback" based on yield results, and do not prevent yield loss. In order to prevent yield decline by "feed-forward" type action targeting yield changes, yield prediction based on operating conditions is essential. In this study, we assumed that yield is synonymous with the strength of the discharged sintered cake, and attempted to apply the porous material strength estimation formula to the sintered cake. The sintered cake was divided into a cake pore part lost by crushing and a sintered ore part as a matrix portion containing pores that remain after crushing, and the formulation of cake porosity and sintered ore strength was studied. Using the amount of melt (melting ratio) generated in liquid-phase sintering and its penetration length into the ore as key factors, the estimation formulas for cake porosity and sintered ore strength were built. In addition, experiments using diffusion pairs were carried out to verify the hypothesis regarding the penetration distance. A pot test were carried out to verify the constructed model , and confirmed a good correlation between the calculated yield by bed temperature measured and the blending components, and the actual measured yield.