Tamahagane is compared to the lance metal with multicolor after extremely low temperature blowing in a test converter using a multifaceted process engineering approach. The following conclusions were reached:

(1) The golden portion of tamahagane consists of an oxide film approximately 20 nm thick, which is composed of three layers. This multilayered oxide film gives tamahagane its "gorgeous" color.

(2) Tamahagane, a high-purity iron, is produced through a metallurgical reaction network consisting of three reactions: a hydrogen production reaction due to the decomposition of moisture in the blast, a reverse water-gas shift reaction, and a carburization reaction due to aging (long-term refining).

(3) The temperature at which tamahagane is formed through this metallurgical reaction network is around the iron point (720°C) of the intersection point between Fe-FeO equilibrium and Boudouard equilibrium and the eutectoid temperature of the iron-carbon system (A1 point: 723°C).

(4) In the case of a weight absolute humidity of 0.0055 (kg-H₂O/kg-dry air) at a base temperature of 10°C, and 0.0085 after adiabatic humidification (compression ratio of 1.1), the carburization time for an average carbon content of iron (total weight of 3 ton) is approximately 10.5 to 16.0 hours.

(5) Humidity of environments where Tamahagane is made is another important factor as well as charcoal reactivity and TiO₂ content in iron sands.

Steelmaking slag, a by-product of the steelmaking process, contains free CaO (f-CaO), which hydrates to form Ca(OH)₂, causing significant volume expansion and disintegration. Basic Oxygen Furnace (BOF) slag with its high f-CaO content exhibits particularly severe expansion. At JFE Steel, steelmaking slag intended for use as subbase course material is treated in a steam aging facility to stabilize expansion and slag expansion after aging is evaluated using the expansion stability test specified in the JIS standard. However, nonuniform steam distribution during aging often prolongs stabilization and increases steam consumption. In addition, some aged slags are not sufficiently stabilized and fail to meet the criteria, requiring re-aging and reducing productivity. This study aims to investigate the mechanisms and causes of delayed temperature rise and steam flow heterogeneity in steam aging facilities. Steam flow heterogeneity was analyzed through laboratory-scale experiments, on-site sampling, and numerical simulations based on actual slag properties. The results revealed that the steam flow heterogeneity arises from ruts formed by heavy machinery and particle size segregation during the slag piling process, with ruts having a greater influence than segregation. These findings indicate that optimizing piling methods is essential for improving steam distribution, reducing energy consumption, and enhancing productivity in steam aging facilities.

A new numerical method to analyze reaction and heat transfer in layered packed bed of layered burden materials was developed. This method combines steady-state simulator of blast furnace operation and "digital basket" model. The digital basket is a fixed bed of burden materials through which the reducing gas flows. The fixed bed can be a mixture or layers of iron ore and coke. The mathematical expression for the digital basket is a subset of blast furnace simulator which consists of one-dimensional conservation equations of mass, heat and chemical species, and rate equations of reactions and heat exchange for gas and burden phases. The reducing gas temperature, composition and flow rate are used as the boundary condition at the bottom of the digital basked. These variables are extracted along a trajectory of descending burden material that is estimated by the blast furnace simulator. This treatment combines the blast furnace simulator and the digital basket model, and allows to reproduce the reaction and heat transfer behaviors of the burden bed descending in the blast furnace. This new method was applied to mixed and layered packed bed of iron ore and coke and successfully revealed the differences in the processes of heating and reduction reaction. The results showed that the deviations of the gas and solid compositions in the burden layer were enlarged under the mixed charging condition compared to the mixed charging. This is due to the separate occurrence of the reduction reaction and the coke gasification.

With the increasing strength requirements for automotive spring steels, hydrogen embrittlement has become a critical issue.

The precipitation of fine ε-carbides has been identified as an effective method in mitigating hydrogen embrittlement. However, precise quantitative evaluation of their size and volume remains essential for effective microstructural control.

In the present study, ε-carbides in spring steel were quantitatively analyzed using small-angle X-ray scattering (SAXS), and the reliability of the results was evaluated. The volume fraction determined by SAXS was compared with the maximum precipitation calculated from solute carbon content, while particle size was assessed based on transmission electron microscopy (TEM) observations.

Specimens of SAE9254 steel were quenched at 950°C and subsequently tempered between 150°C and 450°C. Conventional SAXS analysis, which assumes a single-component fitting, yielded volume fractions that exceeded the calculated maximum. In contrast, the application of a two-component fitting approach, which accounts for scattering contributions from both the martensitic matrix and ε-carbides, produced results consistent with the calculated maximum.

Discrepancies were observed between particle sizes measured by SAXS and TEM, with the divergence increasing at higher tempering temperatures. This discrepancy is primarily attributed to the difficulty in detecting smaller particles using TEM, particularly when the precipitates exhibit a broad size distribution.

These findings confirm the effectiveness of the two-component fitting method and demonstrate enhanced analytical accuracy in the quantitative evaluation of ε-carbides using SAXS.

Sulfur is known as one of the five ubiquitous elements of steel, and the addition of sulfur reduces the performance of steel. Therefore, the sulfur content in steel must be strictly controlled. In this study, we have been focusing on the iron separation–barium sulfate gravimetric method (JIS G 1215-1) specified in the Japanese Industrial Standards (JIS) as an absolute analytical method for the determination of sulfur in steel. In our previous paper, we demonstrated that the rinse process using hot water in JIS G 1215-1 causes dissolution of barium sulfate (BaSO₄), resulting in a significant decrease in recovery. Therefore, suppressing the dissolution of BaSO₄ during the rinse process specified in JIS G 1215-1 has been critical issue in this analytical method. In this paper, we aimed to establish a novel rinsing method to replace the conventional hot water rinsing. As a result, it was found that rinsing with an ethanol solution of acetic acid effectively removed excess Ba²⁺ and Cl⁻ without dissolving BaSO₄. With this novel rinsing method, the conventional problem of reduced recovery caused by the rinse process was resolved, and quantitative recovery of the BaSO₄ precipitate was achieved.

This study aims to clarify the influence of hardness distribution on the pitting fatigue strength of nitrided steels. Gas nitriding with controlled nitriding potential was applied to SCM440H and 31CrMoV9 steels, and roller pitting tests were conducted. The nitrided specimens exhibited superior pitting fatigue strength compared with carburized specimens at 10⁷ cycles, corresponding to the fatigue limit. In contrast, under high contact pressure, early pitting occurred within 10⁵ cycles, indicating reduced fatigue performance in the finite-life. The pitting fatigue strength of nitrided steels strongly depended on the case-hardened depth, and specimens with deeper hardened layers demonstrated higher durability. Under high contact pressure, most of the plastic deformation occurred in the early stage of testing, whereas work hardening developed progressively with increasing number of cycles. In nitrided steels, such plastic deformation induces tensile stress at the contact surface, and in combination with frictional stress, promotes the formation of vertical cracks originating from the compound layer. Therefore, increasing the case-hardened depth is effective for suppressing early pitting by reducing plastic deformation. For nitride steels, pre-running to induce work hardening also mitigated early pitting without reliance on alloying elements or prolonged nitriding durations. These findings indicate that, even when flaking initiates from the surface, the hardened layer depth plays a critical role in the rolling–sliding contact fatigue performance of nitrided steels. Consequently, for components such as gears that operate under rolling–sliding contact, it is essential to consider the influence of internal shear stress in strength design to achieve superior pitting fatigue strength.

Control of trace elements in steel is essential for maintaining material quality, and reliable analytical methods are required to determine their concentrations accurately. The molybdenum blue spectrophotometric method, standardized in JIS G 1212 based on ISO 4829, is widely used for the determination of silicon in steel. Although this method has been employed for many years, several procedural steps still rely on empirical knowledge, and the chemical basis underlying its prescribed conditions has not been fully clarified. In this study, we reassessed the JIS procedure with a focus on the formation of molybdosilicic acid, its reduction to molybdenum blue, and the influence of reaction temperature on analytical performance. UV–Vis measurements showed that β-type heteropolyacid species, exhibiting a single absorption maximum near 810 nm, are preferentially formed around 20 °C, whereas higher temperatures promote conversion to α-type species with reduced absorbance. Calibration curves obtained at 20 °C demonstrated excellent linearity. The validity of the optimized conditions was confirmed by analyses of certified reference materials, in which measured silicon contents agreed well with certified values. These findings provide a scientific rationale for the long-established JIS method and highlight the importance of strict control of reaction temperature and reaction time to achieve reliable and reproducible measurements.

In recent years, it is necessary to reduce CO₂ emissions from the blast furnace, due to prevent global warning. Therefore, low coke ratio operation is required to reduce coke consumption in ironmaking process.

On the other hands, because coke works as a spacer in the blast furnace, low coke rate operation causes various problems, including deterioration of furnace permeability and delay of reduction reaction. Iron ore with low reduction ratio also expects to cause the deterioration of permeability, this is because FeO-containing slag promotes softening and melting of iron ore. Therefore, it is important to quantify the effect of ore melting behavior on permeability.

In this study, the effect of ore contraction behavior on permeability of cohesive zone was quantified by using the cohesive zone simulator, focusing on the difference in contraction behavior due to the difference in reduction ratio. In addition, the effect of ore contraction ratio on the permeability of blast furnace was estimated by the numerical simulation model.

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.

To intuitively understand non-uniform solidification and macrosegregation during continuous or ingot casting, the solidification structure of a transparent ammonium chloride aqueous solution was observed using a bridging-inducing Sato mold. First, using a heat-resistant glass cell equipped with a chill plate, the crystal growth of ammonium chloride dendrites near the chill plate was In-situ observed, and also an appropriate cell design was considered. Furthermore, using a constant flow velocity manufacturing device equipped with an electromagnetic stirrer, the relationship between the dendrite growth behavior and the perpendicular liquid flow velocity was investigated, and finally the flow velocity near the dendrite was estimated inside the mold.

By installing the chill plate and cooling stainless steel plates, the non-uniform solidification conditions was able to reproduced which was observed in actual steel and numerical simulations. At the chill plate, the dendrite growth velocity was relatively uniform. However, at the bottom half of the mold, the growth velocity increased or decreased depending on the observation location and solidification time. The growth velocity of the primary and secondary arms of dendrites, which grew perpendicular to the liquid flow at various velocities, increased almost linearly with increasing flow velocity. Using the relationship between the liquid flow velocity and dendrite growth velocity, the flow velocity near the dendrites could be estimated from the growth behavior such as the orientation and velocity of the secondary dendrite arms.

Electrical resistivity measurement is a powerful method for evaluating the solute carbon concentration (C_sol) in BCC iron. In this study, the effect of carbide precipitation on the accuracy of C_sol quantification was examined by applying a model that predicts the electrical resistivity of composite microstructures containing dilute-dispersed spherical carbides. For Fe–C alloys with spheroidized cementite dispersed in ferrite, C_sol in ferrite could be estimated with an uncertainty of only several tens of ppm. In Fe–0.2Mn–C alloys, high accuracy comparable to that of Fe–C alloys was achieved when Mn enrichment in ferrite accompanying cementite precipitation was properly taken into account. For Fe–2Mn–0.5Si–C martensitic alloys, Mn partitioning, dislocation annihilation, and grain coarsening do not occur during tempering at low-temperature below 573 K. Therefore, changes in electrical resistivity during tempering directly reflected the decrease in C_sol, enabling accurate evaluation when the contribution of carbide precipitation was removed using the spherical dilute-dispersion model. In contrast, high-temperature tempering at 873 K induced pronounced Mn partitioning, and even slight uncertainties in the measured Mn concentration in ferrite led to errors of several hundred ppm in the estimated C_sol. Although errors associated with volume fraction and electrical resistivity of carbides also affected the evaluation, their impact was much smaller than that of Mn partitioning. Consequently, except for the high-temperature-tempered Fe–2Mn–0.5Si–C alloy, the final accuracy of C_sol measurement can be maintained within several tens of ppm when appropriate corrections are applied.

To clarify the mechanisms of plastic deformation and ductile fracture, it is crucial to elucidate the defect-formation processes occurring during plastic deformation. In this study, we performed in situ transmission electron microscopy (TEM) observations of the formation of small prismatic dislocation loops via the double cross-slip of screw dislocations in high-purity iron during tensile deformation at elevated temperatures. Conventionally, the type of a dislocation loop (vacancy or interstitial) has been determined by exploiting the dependence of its image contrast on diffraction conditions, as well as the diffuse scattering patterns generated by the loop in electron diffraction. However, such “static” identification methods are inapplicable to small dislocation loops (approx. <30 nm in diameter) whose image contrast becomes indistinct due to the comparatively large thickness of specimens required for dynamic in situ observations. To overcome these limitations, we propose a new “dynamic” identification method that utilizes the dynamic behavior of a dislocation forming a loop, rather than the intrinsic image contrast or diffuse scattering patterns of the loop itself. Applying this method, we reveal that the dislocation loops formed during tensile deformation at elevated temperatures are of the vacancy type. This finding suggests that loop formation via double cross-slip at elevated temperatures is one of the vacancy-formation mechanisms during plastic deformation, providing important insight into the ductile fracture processes of iron-based materials.

To predict the microstructures of steels, direct coupling of phase-field method and Calculation of Phase Diagrams (CALPHAD) databases is desirable. However, such direct coupling is challenging even for the binary Fe-C system. The first difficulty is that the local equilibrium condition becomes an implicit function, resulting in extremely high computational costs. The second difficulty is that the relationship between phase composition used in phase-field method and site fraction employed in CALPHAD method is nonlinear. In this study, a phase-field model for the Fe-C system is developed by combining Direct CALPHAD Coupling (DCC) model, which explicitly solves the local equilibrium condition, with a chain-rule formulation that links phase composition to site fractions. Numerical tests for δ phase solidification and γ phase peritectic transformation demonstrated that the proposed model satisfies the local equilibrium condition with errors small enough to have no impact on the simulation results and accurately reproduces phase diagram at equilibrium condition. The developed approach provides a framework for simulating microstructure evolution directly coupled with CALPHAD database for steels containing interstitial elements such as carbon and nitrogen.

Silicon is one of the five ubiquitous elements of steel, and the addition of silicon improves the performance of steel. Therefore, the silicon content in steel must be strictly controlled. This paper focuses on the silicon dioxide gravimetric method (JIS G 1212) specified in the Japanese Industrial Standards (JIS) as an absolute analysis method for silicon content in steel. The contamination derived from glassware affected the analysis values. The silicic acid (Si(OH)₄) in the digested solution is in equilibrium with both the silicon dioxide (SiO₂) in the sample and the SiO₂ on the glass surface. Therefore, it was found that the use of glassware in JIS G 1212 plays a crucial role in suppressing the dissolution of silicon from the sample. The elements contained in the steel also influenced the analysis values. Especially, molybdate ion (MoO₄²⁻) in the digested solution, originating from steel samples, not only inhibited the formation of hydrated silica (SiO₂·nH₂O) but also significantly accelerated the dissolution of Si(OH)₄ during rinse. From these results, it was found that molybdenum contained in steel samples reduces the silicon recovery in the silicon dioxide gravimetric method. Silicon recovery in the entire JIS G 1212 was approximately 100% regardless of the steel sample used. This indicates contamination derived from glassware does not affect the recovery of silicon in the total process of JIS G 1212.

A mold was devised to evaluate the macrosegregation caused by solidification shrinkage and bridging by columnar dendritic structures. Casting experiments and numerical simulations of Sn-30wt.%Bi alloys using the devised mold were conducted to investigate the behavior of macrosegregation formation. Bridging due to columnar dendrites formed in the experimental sample, with minor positive segregation and shrinkage cavities forming below this. Numerical simulations reproduced the measured cooling curves, and the distributions of temperature, liquid flow, and Bi segregation ratio during the alloy solidification were analyzed. Consequently, a Bi-segregation region similar to that in the experiment was formed along the centerlines of the sample. During the formation of this segregation, the liquid flowed across the bridging region and toward the bottom. These results confirm that the mold devised in this study can generate macrosegregation (positive segregation) owing to solidification shrinkage and bridging of the columnar dendritic structure.

During the solidification of molten steel, the progression of columnar dendrite growth significantly influences the final microstructure through its morphology and microsegregation behavior. Consequently, comprehending and controlling the formation process of the solidification structure is essential for minimizing casting defects. In this study, we explored the three-dimensional morphology of columnar dendrites and the solute concentration distribution in the liquid phase by employing fluorescence imaging of a ternary solution model material. The solution comprised succinonitrile as the solvent, with water and the fluorescent reagent Lumogen R Yellow 083 (LY) as solutes. We also investigated the impact of solidification rate on columnar dendrite growth. Utilizing a confocal system, we acquired the three-dimensional structure near the dendrite tips, identified its characteristics, and assessed the fraction of solid based on the captured images. Furthermore, by examining the solidification morphology across a range of solidification rates from 0.010 to 0.500 mm s⁻¹, we observed variations in primary arm spacing and the transition from aligned dendrites to superdendrites, determining that each solidification morphology could be explained by the corresponding solidification conditions. Additionally, by evaluating the LY concentration between primary arms at various heights from the primary dendrite axis and distances from the dendrite tip, we demonstrated that it could generally be reproduced by relatively simple solidification models.

Macro-segregation is still an important problem to be solved. To reduce the macro-segregation, suppression of flow during solidification is essential. A magnetic field is a promising candidate because it has a function of flow suppression of en electrically conductive liquid under non-contacting operation. However, relating to the suppression of the flow induced in a solid-liquid mixed region using the magnetic field, only few studies have been done until now. Therefore, in this study, the effect of the magnetic field on the velocity of a liquid tin flowing through a flow channel with or without a solid cylinder in the flow channel produced by alumina or copper has been investigated. In both the alumina and copper flow channels, the velocity decreased as the magnetic field strength increased. This result is qualitatively consistent with the theory of the Hartmann flow. The velocity in the alumina flow channel was proportional to the −0.373 power of the Hartmann number while it was proportional to the −1.86 power of the Hartmann number in a copper flow channel. The former was far away from the theory of the −1 power while the latter was close to the theory of the −2 power. This might be the difference of the entrance length under the magnetic field imposition between the alumina and the copper. The measured flow suppression effect of the magnetic field on the flow in the channel without the cylinder was larger than that with the cylinder under the same magnetic field strength.

A comprehensive thermodynamic assessment of the Fe–P system was conducted based on experimental phase diagram data and thermodynamic properties. The obtained parameters, combined with previously reported parameters for the Fe–C system, were employed to calculate the Fe–C–P ternary phase diagram. To improve the stability of the Fcc phase, additional parameters for the Fcc phase of the P–C system were introduced. For the liquid phase, association model considering Fe₂P and Fe₂C species was adopted. The Fcc and Bcc phases were described using a two-sublattice model with the (Fe,P)₁(C,Va)_0.25.

The Fe–P binary system was successfully reproduced across the entire composition range, including high phosphorus compounds such as FeP₂ and FeP₄. The calculated results successfully reproduced the experimental data for both the phase diagram and thermodynamic properties. Furthermore, for the Fe–C–P ternary system, a satisfactory reproduction of numerous experimental data was achieved without introducing any ternary interaction parameters. The set of parameters obtained from the present model exhibited better agreement with experimental observations compared to those calculations using the regular solution model in the liquid phase.

A simple photometric detector for titration was developed using a white LED and an RGB color sensor as the light source and detector, respectively. This detector could record the color change of the sample solution during titration. The color sensor has 12-bit resolution for each red, green, and blue channel. The detector included a magnetic stirrer, and the controller controlled the mixing of a sample solution. The RGB values were transferred to a PC via a USB port. They were automatically converted to absorbance and L*a*b* data, and the results were displayed as titration curves. However, the volume of titrant added to the sample must be manually entered into the PC. The detector is as compact as 125 mm × 90 mm × 90 mm. First, the analytical performance of the titrator was evaluated by standardizing the EDTA solution with calcium carbonate. Then it was applied to the determination of chromium ions in synthesized steel samples according to the method indicated in JIS G 1217:2017, Annex 1 (normative). This method uses ammonium peroxodisulfate oxidation followed by potassium permanganate titration. This detector's function is not only helpful for objectively identifying the endpoint of a titration but also valuable for transferring the veteran's skill in endpoint determination to a novice technician, since subtle color changes can be recorded as numerical data.

Reliable prediction of macrosegregation requires accurate thermophysical properties that govern melt flow, particularly the thermal expansion coefficient β_T and kinematic viscosity ν. However, these properties are difficult to measure with sufficient accuracy. In this study, we develop a data assimilation approach that combines the modified lattice Boltzmann method (MLBGK) with a particle filter to estimate β_T and ν using only thermal analysis data. A two-dimensional system with a horizontal temperature gradient was considered, and twin experiments were performed to evaluate the feasibility of the method. The results show that both β_T and ν can be estimated with high accuracy. In single-parameter estimation, convergence to the true value was achieved rapidly for particle numbers N ≥ 200. Simultaneous estimation was also successful. The estimation accuracy depended on the number of measurement points and the filtering interval, and estimation of β_T is generally more accurate than ν. The proposed approach provides a practical means of determining flow-related properties of molten steel from thermal analysis measurements.

A microfluidic titration method using a cross-type microchannel device was developed for to the determination of total iron in steel samples. The redox titration reaction proceeded within the microchannel, and the titration endpoint was determined based on the differential value of grayscale intensity derived from blue-channel image analysis. The reaction behavior was visualized in real time, enabling quantitative evaluation of concentration-dependent color changes. Optimization of the flow rate and observation point revealed that a flow rate of 0.05 mL min⁻¹ and a detection position 1.5 cm downstream from the junction yielded the highest sensitivity. The obtained calibration plot exhibited a semi-logarithmic relationship with iron concentration. When applied to the certified reference material JSS 831-2 Taharoa iron sand, the total iron concentration determined by the microfluidic method (46.9 ± 1.9 mM) was statistically indistinguishable from that obtained by the conventional volumetric analysis based on JIS M 8212 (45.49 ± 0.18 mM), as confirmed by a t-test. These results demonstrate that the proposed system achieves analytical accuracy comparable to traditional wet chemical methods, while eliminating subjective endpoint determination, reducing sample and reagent consumption, and enabling automated and reproducible operation. The results demonstrate the feasibility of integrating redox titration within a microchannel as a new approach to miniaturized, automated wet analysis. The microfluidic titration platform offers a promising approach for miniaturized, automated wet analysis and has potential for extension to other volumetric techniques such as chelatometric and acid–base titrations.

Semi-solid deformation strongly influences the formation of casting defects, and understanding its governing factors is essential for improving the quality of cast products. In this study, we develop a method to systematically evaluate the influence of grain morphology on semi-solid deformation behavior using multi-phase-field lattice Boltzmann simulations. Cross-shaped grain morphologies are artificially generated, and two approaches—compression and growth—are introduced to create semi-solid mixtures with a wide range of solid fractions. Semi-solid simple shear deformation simulations reveal that deformation proceeds through grain–grain sliding and rearrangement when grain circularity is high, whereas grain clusters form and their rotation govern deformation when circularity is low. Furthermore, lower circularity leads to the formation of larger clusters that are less likely to rotate. These findings demonstrate that grain morphology is a key factor strongly affecting semi-solid deformation behavior. In addition, the proposed methodology is shown to be effective for systematically evaluating semi-solid deformation with respect to both grain morphology and solid fraction.

Among the internal defects of cast steel products, the center segregation deteriorates the ductility and fatigue strength of high strength steel. Therefore, exact understanding of formation mechanism of center segregation and development of the countermeasure technologies are necessary. Kurosawa et al. reported that iron-phosphide could be observed in the center-segregated region of high phosphorous and hyper-peritectic steel slabs. However, the precipitation mechanism of iron-phosphide has not been fully clarified. Therefore, in this study, in order to clarify the precipitation mechanism of iron-phosphide in the final solidification of CC slab, the melting behavior of the center segregation region of high phosphorous and hyper peritectic steel slab has been investigated by using high temperature observation equipment installed with the image furnace. Additionally, the enrichment of solute in the inter-dendritic region and the further enrichment of solute element during the final solidification was modelized by using micro and macro segregation model. In Fe–C–P ternary eutectic solidification system, the effect of phosphorous concentration on the precipitation mechanism of iron-phosphide during the formation of center segregation was discussed.

A coarse-grained (CG) molecular dynamics (MD) model for alloy systems was developed and applied to Al–Cu alloy system. Large-scale CG-MD simulations of crystal growth were systematically conducted under various solute concentrations and temperatures of undercooled melts using a supercomputer. The results showed that, for all concentrations studied, the growth velocity increased with decreasing temperature, reached a maximum at the undercooling of ΔT = 225 K, and then decreased at lower temperatures, yielding a peak-shaped temperature dependence. Regarding morphology, rhombic crystals with strong anisotropy were observed at medium to high temperatures for pure Al and Al–1.3at%Cu, while weakly anisotropic circular crystals formed at the undercooling of ΔT = 275 K. In contrast, Al–3.0at%Cu produced weakly anisotropic structures across all conditions. Despite the reduced resolution inherent in CG compared to all-atom (AA) MD models, performing numerous AA simulations at the micrometer scale remains practically unfeasible even with current supercomputers. This study demonstrates that CG-MD provides a powerful and effective approach for exploring the temperature- and concentration-dependent solidification processes in alloy systems, highlighting its significant potential for large-scale materials simulations.

The liquidus and solidus temperatures of the Fe–Ni system were determined by differential scanning calorimeter. In addition, thermodynamic reassessment of the phase diagrams and thermodynamic properties of Fe–Ni, Fe–C, and Ni–C systems was performed based on literature data and present results. The Gibbs energy of the liquid phase of Fe–C and Ni–C systems was approximated using the association model. The Gibbs energies of the Fcc and Bcc phases were approximated using a two-sublattice model of the (Fe,Ni)₁(C,Va)_0.25 structure. The calculation results were able to reproduce various experimental data. Furthermore, two-phase separation of the Bcc phase in Fe–C and Ni–C at low temperatures were predicted, and this trend is consistent with experimental data. On the other hand, the unreasonable two-liquid separation and the stabilization of the Bcc phase at high temperatures calculated in previous studies were not calculated.

The phase diagrams of the Fe–Ni–C ternary system were also calculated using the parameters of the binary system obtained in this study. All experimental data could be reproduced without introducing ternary parameters. Thus, the model used in this study is suitable for development of a multicomponent database.

In this study, we investigated the surface properties of iron subjected to corrosion in contact with frozen salt solutions, focusing on the effects of solution aeration and salt type on ferrous iron dissolution behavior. X-ray photoelectron spectroscopy (XPS) was used to examine the surface conditions after corrosion. Image analysis of the frozen media indicated that dissolved oxygen in freeze-concentrated solutions (FCS) plays a crucial role in the dissolution process. XPS analysis confirmed the formation of iron hydroxide and iron oxyhydroxide on the iron surface, suggesting a reaction mechanism similar to that observed under atmospheric conditions. Additionally, surface analysis revealed that specific salt ions—such as F⁻, Cl⁻, and Cs⁺—exhibit a tendency to adsorb onto the iron surface under conditions of pronounced dissolution. These hard anions form complexes with Fe (II) ions, thereby promoting their dissolution. Moreover, Cs⁺ ions readily adsorb onto FeOOH, creating a concentration gradient near and beyond the iron surface that further promotes iron dissolution.

The effect of cooling rate on distribution of Cu and S concentration at residential levels in low iron carbon steel was investigated to discuss the formation mechanism of fine copper sulfide precipitates. Quenching molten samples for Fe-0.1mass%Cu-0.02mass%S-0.1mass%C and Fe-0.1mass%Cu-0.1mass%S-0.1mass%C were conducted with water (WQ), flowing water (FWQ), air (AQ), argon gas (ARQ) and furnace (FQ). Subsequently, the samples were analyzed for the composition of precipitates and the distribution of Cu and S concentration of the iron matrix. Increasing cooling rate increased molar ratio of Cu to S in precipitates as decreasing S concentration, indicating that higher cooling rate would cause less formation of iron sulfide of the precipitates. Moreover, the distribution of Cu concentration over the solidification fraction was reproduced with the Clyne–Kurz segregation model regardless of cooling rate; however, below 99% solidification fraction, the S concentration of the WQ sample was higher and increased more moderately than the Scheil model while that of the FQ sample was close to the Scheil model. The sulfur of the WQ samples was supposed to form finer sulfides dispersed in the iron matrix than the FQ samples. Thus, the precipitation of fine copper sulfide in solid iron is probably due to fast cooling rate, which more suppresses local segregation of sulfur and prevents the formation of sulfides other than copper sulfide.