Hydrogen-rich blast furnace ironmaking is an important low-carbon technology to reduce CO₂ emissions of steel industry, and its effect on softening-melting performance has a great influence on blast furnace ironmaking. In this paper, the softening-melting properties of basic pellets with hydrogen-rich based on high pellets ratio ironmaking were studied. The microstructure evolution and softening-melting mechanism of pellets during the process were investigated. The results show that when the hydrogen concentration increases from 0% to 12%, the initial softening temperature (T₁₀) decreases from 1209°C to 1197°C, the melting starting temperature (T_s) and dripping temperature (T_d) increase respectively, which means bottom the cohesive zone descends. S-value decreases from 458.55kPa·°C to 293.33kPa·°C. In hydrogen-rich condition, hydrogen will not gather on the surface of pellets like CO to form a dense iron shell. More FeO is produced on the surface and inside of pellets, which forms the low-melting-point slag phase with gangue and reduces the initial softening temperature. And after entering the melting stage, the FeO produced inside decreases, resulting a high melting point of slag, So, the dripping temperature increases from 1412°C to 1458°C.

The paper focuses on DP980 dual-phase steel, aiming to deeply investigate the evolution and control strategies of residual stress during the run-out table cooling process. The temperature-phase transformation coupling model was solved using the finite difference method, and the viscoelastic-plastic constitutive relationship model considering stress relaxation was solved using LU decomposition. A rapid calculation model for shape during laminar cooling of DP980 was established and validated for accuracy using industrial actual data. Based on this model, the impact of different operational conditions on the residual stress in the strip was analyzed. The results indicate that smaller initial temperature difference and initial shapes such as middle-wave or quarter-wave lead to lower edge compressive stress in the strip. In addition, the sparse cooling and off ultra-fast cooling also help to alleviate the problem of excessive compressive stress at the edge of the strip. However, implementing rear section cooling may result in uneven stress distribution in the width direction of the strip, with a greater degree of stress reduction near the edges. Based on the analysis of stress impact laws, improvements were made to the original production line processes. These improvements reduce residual stress and effectively mitigate wave-shaped defects during the laminar cooling on the run-out table.

Compression tests of self-fluxing pellets were conducted at 300 K and high temperatures with prismatic test samples cut from the centre of pellets. Two types of pellets were used: one reduced with CO, and one reduced with H₂. Prismatic-shaped specimens were fractured in a brittle manner during the compression tests at 300 K and 973 K. The fracture stress at 300 K of the specimen reduced with CO is nearly the same as that reduced with H₂ while the fracture stress at 973 K of the specimen reduced with CO is higher than that with H₂. They show plastic deformation at higher than 1173 K. The yield stress of both types of specimens is nearly the same at above 1173 K. Poisson's ratio varied during deformation, suggesting deformation mechanism changes as deformation proceeded. The strain distribution of a specimen deformed at 1273 K measured using digital image correlation showed plastic deformation accumulated near the pores. It is considered that not only the collapse of the pores but also the plastic deformability of the matrix itself influences the temperature dependence of the yield stress of pellets.

Induration is a thermal treatment process wherein the green pellet properties are enhanced for subsequent reduction processes such as blast furnace and DRI production. During induration, the pellet essentially undergoes (i) physical change, that is, particles sinter with each other imparting strength to the pellet and (ii) chemical change by which phase change occurs either due to reduction/oxidation or thermal decomposition. Both these changes are interdependent. In case of induration of magnetite pellet, the exothermic oxidation of magnetite to hematite generates heat within the pellet. However, for the induration of hematite pellets carbon in the form of coke breeze is added in the green pellet mix to aid heat generation by combustion within the pellet.

In this paper, the sintering of single hematite pellet is investigated isothermally using optical dilatometer. Sintering kinetics is deduced for the pellet and the effect of coke addition on sintering kinetic parameters has also been investigated. The shrinkage data, expressed in terms of sintering ratio, from the optical dilatometer is sufficient to capture sintering kinetic. The extent of sintering under isothermal condition as a function of time can be expressed in terms of power law relation as Ktⁿ. The constant K as function of sintering temperature, as sintering being a thermally activated process, can be described using Arrhenius equation. The kinetic triplet namely, time exponent(n), pre-exponential factor(kꞌ) and the activation energy(Q) are determined for pellets with no coke to 2 wt% coke addition. This paper presents insight into the sintering mechanism of hematite pellet.

Recycling of Scrap will lead to the continuous accumulation of residual element Tin (Sn) in steel production. The influence of Sn on interstitial-free (IF) steel and the formation of Sn compounds were investigated by experiments. The types of inclusions in IF steel with Sn is TiN, Al₂O₃, MnS and Ti₂S₃, which are consistent with those in IF steel. After adding Sn from 0% to 0.5%, the starting solidification temperature of molten steel decreases, resulting in the increase of inclusion number density. The average size of inclusions decreases from 2.39 μm to 1.89 μm. After adding 0.065%La, the inclusions containing Sn, such as La-Sn, La-Sn-O and La-Sn-Ti, generate in IF steel with 0.1%Sn or 0.5%Sn. With the increase of Sn content in IF steel containing 0.065%La, the number density of inclusions decreases and the number of large size inclusions containing Sn (≥10 μm) increases from 121 inclusions to 284 inclusions. Furthermore, the addition of Sn and La refines the macrostructure of ingots. Thermodynamic calculation shows that La₂Sn and La₅Sn₄ inclusions can form during the solidification process in sample with 0.1%Sn and 0.065%La. And in sample with 0.5%Sn and 0.065%La, La₂Sn and La₅Sn₄ inclusions can form directly in the molten steel. The generation of inclusions containing Sn can change the existing state of Sn and is beneficial in inhibiting the grain boundary segregation of Sn. The experiment lays a theoretical foundation for the use of La to minimize the harmful effects of Sn in IF steel in the future.

The simulation results for the E250 B0, S355J2, and X70M grades provide valuable insights into the effects of material thickness, deformation, and alloying elements on strain accumulation and microstructural evolution during the rolling process. For E250 B0, the low recrystallization temperature and minimal alloying led to moderate strain accumulation, with the highest reductions occurring above the RLT. In contrast, S355J2, with the addition of Nb, exhibited increased strain accumulation due to the precipitation of Nb(C,N), which enhanced the material's resistance to deformation, especially in thinner specimens. The X70M grade, with a higher Nb content, demonstrated a more pronounced strain accumulation, particularly in the thicker specimens, due to the reduced recrystallization and the influence of strain-induced precipitation. Thinner specimens experienced more intense deformation and faster recrystallization, resulting in finer grains and higher strain accumulation. Meanwhile, thicker specimens underwent slower deformation and recrystallization, promoting grain growth and reducing strain accumulation. The study highlights the critical role of material composition, thickness, and processing parameters in controlling strain accumulation, microstructural homogeneity, and the final properties of the rolled products. The presence of Nb was particularly influential in improving strain resistance and refining the microstructure, which is essential for achieving optimal material performance.

The warm V-bendabilities and hydrogen embrittlement properties of ultrahigh-strength Quenching and Partitioning (QP)-Transformation-Induced Plasticity (TRIP) steel sheets were investigated to apply the QP-TRIP steel sheets for automotive structural parts manufactured by cold or warm press forming. V-bending tests were carried out at a crosshead speed of 1 mm/min at V-bending temperatures of 25, 100 and 150°C using a hydraulic servo testing machine with a 88-deg. V-punch (punch tip radius R = 2 mm, R/t₀ = 1.7) and a V-dice (dice groove size l = 12 mm, dice shoulder diameter 0.8 mm) using V-bend specimens with dimensions of 5-mm width, 50-mm length and 1.2-mm thickness without and with hydrogen charging. Hydrogen charging was conducted by means of cathodic charging using a 3 wt% NaCl + 3 g/L NH₄SCN solution at a current density of 10 A/m² for 48 h before V-bending. The main results were obtained as follows.

(1) QP-A steel enabled to conduct V-bending at a V-bending temperature T = 25°C although the bending angle after unloading (θ₂) was less than 90-deg.

(2) When V-bending tests were carried out at T = 100°C, QP-B, C, and E steels without hydrogen and QP-B steel with hydrogen charging enabled to conduct V-bending. In addition, QP-B steel was also possible to carry out the V-bending at T = 150°C. These results implied that the V-bending at warm temperatures can improve the V-bendabilities of the QP-TRIP steels.

This study investigated the mechanism of cementite formation in JIS-SCM440 low-alloy steel subjected to high-temperature nitriding (NH) at 913 K, followed by quenching and aging. Specimens with and without prior quenching and tempering (QT) treatment were analyzed to understand the influence of the initial microstructures on cementite precipitation. Comprehensive characterization using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and electron probe microanalysis (EPMA) revealed that NH treatment promoted significant nitrogen diffusion into the steel matrix, resulting in the formation of a nitrogen compound layer and a hardened nitrogen martensite layer beneath the compound layer. In the NH specimens following QT treatment (QTNH), accelerated carbon diffusion to the surface led to cementite precipitation around the surface pores owing to the dissolution of fine carbides. Cementite enhanced the surface hardness of the porous regions compared to that of the NH specimens.

Steel Slag Hydrated Matrix was developed by mixing steelmaking slag as an aggregate with ground granulated blast furnace slag as a binder. In this study, a direct casting process from molten slag was investigated as an alternative to the complicated and expensive Matrix manufacturing process. However, cracks that occur during casting can reduce strength. To prevent crack formation, the mechanism of thermal stress crack initiation and the appropriate conditions for casting molten slag in rock form were investigated by casting experiments, sound measurements, and thermal stress analysis. Compared with slag cooled in the mold, the slag cast under the optimum cooling condition suppressed cracks and did not cause cracks inside the slag. The crack sound was measured by sound measurements. To suppress cracks, it was suggested that a uniform temperature in the slag should be achieved quickly within 10 min after slag injection. The required solidification shell thickness could be estimated based on the tensile stress that occurred on the slag surface. The casting experiments and thermal stress analysis revealed the cooling conditions for suppressing thermal stress cracks in slag casting. Specifically, it was found that thermal stress cracks can be avoided when the molten slag is poured into the mold and then is demolded at the stage where the solidification shell thickness sufficiently exceeds the strength of the slag surface against tensile stress applied to the solidification shell. The solidified slag is thermally insulated, and the temperature inside the slag is uniform and cools while remaining uniform.

Microsegregation of solute components during the solidification process leads to solute pile-up in the liquid phase, which considerably influences the formation behavior of inclusions. However, no quantitative evaluation of solute concentration distribution during dendritic growth has been conducted. In this study, we established an in-situ observation method for quantitatively evaluating solute concentration distribution using model materials with fluorescent reagents to clarify how solute pile-up progresses owing to microsegregation. In addition to evaluating the physical properties of the model materials required for this study, we successfully realized a quantitative evaluation of solute concentration distribution during dendritic growth. Numerical analysis, considering the equilibrium partition of solute components and solute diffusion in each phase, reproduced the measured solute concentration distribution in the liquid phase. Thus, the solute concentration distribution was evaluated through both actual measurements and numerical analysis, demonstrating that a relatively simple model can represent the progression of microsegregation.

Multi-phase steels are often used to realize a combination of high strength and toughness and/or ductility. To optimize their mechanical properties, it is vital to accurately evaluate the grain size, hard phase size and distribution, and dislocation density. In this paper, we studied a new method for evaluating the morphology and phase fraction of the hard phase, i.e., the martensite-austenite constituent (M-A), which is an important component that governs the mechanical properties of high strength steels. Using a scanning electron microscope, martensite can be selectively visualized with a bright contrast by collecting high-angle backscattered electrons. This method identifies only martensite in isolation from other phases, whereas both martensite and austenite are highlighted with the conventional two-step etching method. In addition, machine learning image analysis allows accurate extraction of martensite even in the presence of inhomogeneous backscattered electron image contrast in the matrix. This method provides an accurate and simple evaluation of the morphology of martensite in multi-phase steels over a large area.

For the differences in composition and proportions of input materials, end-point quality requirements and slagging specifications, it is difficult to construct a generalized model to guide steelmaking production. There is a complex connection among different heats in BOF, and this combination of correlations can be thought of as a hidden working pattern. A method named "attribute level division" is developed to exploit the correlations among heats to construct the graph of heats. The model based on the combination of label propagation algorithm (LPA) and back propagation neural network (BPNN), LPA-BP, is proposed for end-point carbon content prediction in BOF. LPA is used to discover the different community in the graph of heats and BPNN is trained to construct different models for end-point carbon content prediction for the heats from different community. The results of comparative experiment show that the LPA-BP model is higher than the baseline 2.5% when prediction error is within ±0.012%. The LPA-BP model also outperforms in some metrics, such as RMSE, MAE. This model provides a novel idea to improve the endpoint hit rate by distinguishing different communities to uncover the hidden working patterns among heats and constructing different models.

In hydrogen-enriched blast furnace operations, the cohesive zone's coke slits are expected to thin, requiring precise control. The softening behavior of lump ore, iron ore sinter, and pellets is influenced by factors such as reduction degree, gangue composition, and slag viscosity. This study investigates the softening and shrinkage mechanisms of hydrogen-reduced pellets, offering insights into cohesive zone behavior in hydrogen-enriched conditions.

A load-softening test system with rapid heating and cooling capabilities was used to evaluate the softening temperature range of pre-reduced pellets in an inert N₂ atmosphere. Self-fluxed and acidic pellets were pre-reduced to 70% and 90% using CO and H₂ gases. Structural changes during softening and shrinkage were analyzed using optical microscopy on interrupted samples, with precise temperature control and force application to measure contraction rates.

Results revealed distinct shrinkage behaviors between self-fluxed and acidic pellets under CO and H₂ reduction. Acidic pellets showed greater and more consistent shrinkage in H₂, while CO-reduced pellets exhibited gradual shrinkage at higher temperatures. Molten slag, forming around 1050°C, significantly influenced shrinkage. Structural analysis highlighted variations in metallic iron and wüstite distributions, with CO-reduced pellets exhibiting a wider mixed region and pronounced sintering at elevated temperatures.

Pellets with thicker metallic shells and higher reduction degrees showed greater deformation resistance under high-temperature loading. The mixed metallic iron and wüstite region's thickness decreased during softening, correlating with molten slag formation. These findings underscore the critical role of mixed region deformation and slag generation in determining the softening behavior of reduced pellets.

Green hydrogen is seen as crucial for the decarbonisation of the economy. Yet, some regions may lack local producing capability, necessitating hydrogen imports. Ammonia can be a cost-effective solution to indirectly transport hydrogen. Three concepts are presented for using ammonia as reductant in the Blast Furnace (BF) process. The first concept, called EASyMelt shaft, incorporates cracked ammonia into the furnace's shaft. The second concept, NH₃ EASyMelt, takes the changes a step further and injects cracked ammonia in both the bosh and shaft tuyeres. The cracked ammonia, heated by plasma torches, replacing hot blast and coal in the bosh tuyeres. Finally, NH₃ EASyMelt is implemented with top gas recycling (TGR). The furnace operation under these scenarios is compared to conventional operation using a multi-phase BF process model. The CO₂ emissions are found to be reduced by 15% for EASyMelt shaft, 60% for NH₃ EASyMelt without TGR and 55% with it. The new concepts are also shown to have a significant impact on the thermal state, gas distribution, pressure drop and cohesive zone characteristics. The study sheds light on how ammonia could be integrated into the BF process, and the expected impact on the furnace thermochemical state and the CO₂ emissions.

The concentration dependence of the activity coefficients of solutes in molten iron is expressed in terms of interaction parameters. The interaction parameters were determined by the experiments under thermodynamic equilibrium and the evaluation had been based only on the accuracy of the experiments. An evaluation of the interaction parameters is proposed due to the thermodynamic stability of homogeneous solution, and is applied to several interaction parameters of the solutes of O, S, Ca and Al in molten iron at 1600°C.

Flotation dryer systems are widely used to dry liquid layers on substrates such as films, paper and steel strips, and many reports discussing design optimization for better heat transfer characteristics and strip stability are available.

As an advantage of this type of system, surface defects caused by contact between a support roll and the strip are prevented by floating the strip with a jet flow. However, since the friction force between the jet flow and the strip is smaller than that between a support roll and strip, flotation systems are prone to strip walking.

This tendency is noticeable in case of bad shape strip. Thus, it is important to improve the strip centering force. To our knowledge, no systematic in-depth study on prediction of the strip centering force with flotation dryers exists in the literature, and in particular, literature which compares experimental and analytical results is very rare.

In the present study, the centering force acting on a steel strip in a flotation dryer was investigated by experiments and simplified two-dimensional fluid analyses in order to evaluate the influence of the side plate geometry and the off-center value from the center of the floatation dryer on the centering force.

The centering force in the experiment and analysis showed a good correlation. Therefore, it is thought that the centering performance of actual floatation dryers can be estimated by simplified experiments and analyses.

Converter completion time delay caused by uncertain events is one of the most frequent disturbances in the steelmaking-continuous casting process (SCCP) with a significant negative impact on the SCCP scheduling. Existing rescheduling methods fall short in providing a comprehensive analysis and evaluation for the production status and disturbance levels, resulting in the scheduling scheme with limited adaptability to on-site environments. This paper addresses this challenge by proposing a dynamic evaluation method for converter scheduling disturbance based on processing time prediction and disturbance influence process analysis. The proposed method consists of three steps that solve the disturbance evaluation problem by predicting the converter processing time, analysing the delay impact of the converter completion time, and solving the real-time procedure buffer capacity. This enables the dynamic scheduling of the SCCP to accurately judge the current operating rhythm and production status, and to achieve precise decision-making for scheduling. Computational experiments based on the actual case from the Chinese steelmaking plants demonstrate the accuracy and effectiveness of the proposed method in large-scale SCCP dynamic scheduling processes. Compared with other methods, the proposed method can effectively reduce the number of rescheduling in production and the deviation of the production process from the initial scheduling scheme by reasonably selecting the scheduling repair strategy, which improves the adaptability of the scheduling scheme to the actual production environment.

The solid–liquid interface energy anisotropy of Zn alloys remains poorly understood. Recently, characteristic 14-arm dendritic growth has been observed using time-resolved X-ray computed tomography at SPring-8 during the solidification of a Zn-4mass%Al alloy. This study investigates the dependence of the dendrite morphologies of Zn alloys on solid–liquid interface energy anisotropy through systematic phase-field simulations of the growth of an isolated equiaxed dendrite. We also develop a data assimilation system to estimate the anisotropy parameters of solid–liquid interface energy and crystal orientation in Zn alloys and validate the system through twin experiments. This study provides insights into the solidification of Zn alloys and a powerful tool for their investigation.

To understand the relationship between the thermal conductivity of the mold flux and its composition from the perspective of the local structure, the thermal conductivities of CaO-BO_1.5-AlO_1.5-SiO₂ melts were measured using the transient hot-wire method in the range of 1573-1773 K, and structural analyses were conducted using magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. Additionally, the covalency of the bonds between each cation in this system and the oxygen atom was evaluated using first-principles calculations to consider the propagation of phonons between each bond. As a result, the degree of polymerization of the network structure, D_P, was calculated from the composition and results of the MAS-NMR analysis and confirmed to have a positive effect on thermal conductivity. Some samples exhibited low thermal conductivity despite a high D_P below 1673 K, owing to the formation of boroxol ring structures. Using first-principles calculations, the covalency of the B-O, Al-O, and Si-O bonds was evaluated quantitatively as the length between the center of the bonds and the center of the electron distribution, L. The standard deviation of covalency in the entire network of a sample, S_L, was obtained and confirmed to have a negative effect on thermal conductivity because a difference in covalency between bonds caused phonon scattering. Finally, by integrating our previous research, the ratio of D_P/S_L was confirmed to be an effective index for evaluating the thermal conductivities of the CaO-BO_1.5, BO_1.5-SiO₂, CaO-AlO_1.5-SiO₂, CaO-BO_1.5-SiO₂, CaO-BO_1.5-AlO_1.5, and CaO-BO_1.5-AlO_1.5-SiO₂ systems.

The quality of iron ore is expected to change, and blast furnace raw materials will diversify in the future as ores are pretreated to improve ore quality. Furthermore, an increase in the proportion of hydrogen-based reducing agents is necessary to satisfy the demand for carbon neutrality. Therefore, the capacity of blast furnace operations to adapt to these external factors must be enhanced. For stable blast furnace operation even when the external factors change, controlling the cohesive zone is crucial. In this study, the ore-packed beds composed of different ores were reduced by heating up to 1200°C in the atmosphere of a hydrogen-enriched blast furnace. Subsequently, the temperature was increased to 1450°C in an inert atmosphere to investigate the softening and melting behaviors of the samples in contact with different ores. During reduction up to 1200°C, metallic iron was bound between ore particles, while no interparticle migration of gangue components occurred. The unreduced oxide core of the ore melted on heating up to 1450°C, although deformation of the ore did not progress considerably owing to the metallic iron structure. The oxide in the reduced metal shell partially melted, and interdiffusion of the gangue components occurred more than 2 mm from the particle interface.

In iron ore sintering, the green bed properties and sinter productivity are influenced by the ore blend mixture including the proportions of ultrafine iron ores in the blend. In this work, iron ore granules, green bed properties and sinter productivity were investigated for blends containing ultrafine iron ores. The granulation and sintering experiments were conducted in a granulation drum with an internal diameter of 500 mm and a length of 310 mm, and a steel pot with an internal diameter of 108 mm and a height of 500 mm, respectively. The results of this study show that the reference blend was representative of a commercial sinter plant mixture in terms of comparable granule size and green bed properties at a similar moisture content of approximately 7%. An increase in the proportion of ultrafine iron ores in the blend resulted in a deterioration of green bed properties. A simple correlation was derived to link green bed voidage (ε) to α, the ratio of granule SMD and dry sinter feed SMD, as ε=0.343exp(1/α). This equation provides a simple yet effective expression that relates green bed voidage to both sinter feed size and granule size, enabling the prediction of bed voidage with a level of accuracy that is comparable to Hinkley's equation. It was concluded that an increase in the proportion of ultrafine iron ores has a negative impact on green bed properties and causes a decrease in the gas flow rate during sintering. Consequently, the productivity of the sinter pot decreased.

This study investigates the viscoelastic properties and the transition behavior between the liquid and solid of polyethylene beads dispersed in silicone oil and silicone oil-water mixtures, simulating the flow behavior of a layered structure consisting of iron ore and a coke bed with derived melts. Oscillation tests revealed that all samples exhibited elastic responses at small strains, transitioning to viscous responses at higher strains. Higher viscosity of silicone oil led to reduced strain at the onset of flow, indicating enhanced lubrication between solid phases. Creep tests showed minimal strain under low stress but significant strain increase over time at high stress, suggesting that the system can achieve a more fluid-like state over an extended period. These findings highlight the impact of liquid viscosity and phase fraction on the mechanical properties of complex multiphase systems.

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.

We have developed experimental and data analysis techniques of imaging XAFS (X-ray absorption fine structure) and investigated the Fe chemical state distribution in iron ore sinters over a field of view wider than 10 mm. Detailed spectral interpretation was provided for oxides and calcium ferrites at different stages of reduction. At lower temperatures, crack-driven propagation of reduction reaction was observed to penetrate deeper than 1 mm, while fine-grain primary hematite underwent reduction without forming cracks. Once the reduction of calcium ferrites begins, the reduction reaction changes to relatively uniform propagation, independent of mineral phases, resulting in a layered distribution of Fe chemical states.

The interaction of hydrogen with lattice defects plays a crucial role in the hydrogen embrittlement mechanism, but the origin of hydrogen-related defects remains unclear. In this study we investigate the formation process of hydrogen-induced vacancies in austenitic stainless steel SUS 304 by positron annihilation lifetime spectroscopy. Positron lifetime measurements of hydrogen-charged samples subjected to tensile testing by different strains show that the formation of hydrogen-induced vacancies first appears when a strain of about 5% is applied. Electropolishing of the hydrogen-charged layer reveals the generation of vacancy-hydrogen complexes in the bulk underneath the hydrogen-charged layer, which develop into vacancy clusters by further application of stress. From the PALS results and complementary X-ray diffraction analysis, the dislocation density required for the formation of hydrogen-induced vacancies is quantitatively determined. Clarification of the conditions for the formation of hydrogen-induced vacancies provides important input and reference data for models of the hydrogen embrittlement in stainless steels.

RH is one of the essential secondary refining processes, and the oxygen lance plays a significant part in its multi-functionalization. Therefore, it is necessary to dig deeper into the jet characteristics at low ambient pressure. This study examined the supersonic oxygen jet parameters, such as the jet Mach number, dynamic pressure, turbulence kinetic energy, and half-jet width with computational fluid dynamics, for RH vacuum furnaces operating at ambient pressures ranging from 4000 to 1000 Pa and 101325 Pa. Underexpanded jets were observed at the ambient pressures from 4000 to 1000 Pa, and single strong barrel shocks existed. It was shown that decreasing the back pressure significantly improved the axial and radial Mach number of the jet. However, this improvement was related to a sacrifice of the dynamic pressure. The length of the potential core region and supersonic region increased greatly with decreased ambient pressure. The decrease in ambient pressure also considerably increased the turbulence kinetic energy, indicating a heightened level of energy transfer. However, the correlation between the half-jet width and the ambient pressure was not a simple linear relationship. The half-jet width increased with the ambient pressure decreasing from 4000 Pa to 1000 Pa.

The morphology, number, and distribution characteristics of inclusions influence the application properties of sulfur-alloyed free-cutting steels. Herein, the three-dimensional morphology and distribution characteristics of MnS inclusions as cast and rolled were systemically explored by X-ray micro-CT. Firstly, based on the composition test and applying the Ohnaka model, the element segregation behaviour and its relation to the morphology of MnS inclusions in steel billets were elucidated. Secondly, the growth of MnS in the steel billet was analyzed using the second-phase precipitation theory. The calculation results show that MnS was generated when the solid phase fraction f_S=0.56, and the relationship between the content of elements and the morphology and distribution characteristic of MnS was established. Thirdly, the characteristics of MnS inclusions transform with various deformation amounts were investigated, and the relative plasticity of MnS reached the peak value when the deformation amount was 50%. Finally, the genetic characteristics of MnS inclusions as cast and rolled were analyzed. In practice, a series of measures composed of increasing the cooling intensity of continuous casting and rolling the billet in the range where MnS has relatively low plasticity was suggested to optimize the product machinability.

A novel solid-state joining method called Cold Spot Joining (CSJ) has been successfully developed. In this joining concept, the material near the joining interface is plastically deformed under high pressure to form a joining interface, resulting in the fragmentation of oxide films at the joining interface and the formation of strong interface. Medium carbon steel sheets were CS-joined under various process conditions. The joining temperature can be varied by the applied pressure during CSJ. Microstructural observations and hardness distribution indicated that the appropriate pressurization resulted in joining temperatures below the A₁ point and suppressed the formation of the brittle martensitic structure. By providing appropriate applied pressure, sound S45C spot-welded joints were successfully produced, showing plug failure of the base metal in both tensile shear and cross-tension tests. Further investigation into the mechanism of interface formation reveals that the oxide film at the interface is fragmented and expelled. At the same time, dynamic recrystallization occurs at the interface and extremely fine new grains with dispersed fine cementite are formed at the interface to achieve the sound joining with sufficient strength.

The Hall–Petch coefficient, which is the slope of the Hall–Petch relationship, was investigated as a means of increasing the yield strength of ferritic steels through highly efficient grain refinement strengthening. Because the Hall–Petch coefficient increases with the grain boundary segregation of solute elements such as carbon, the equilibrium grain boundary segregation behavior was theoretically calculated using the Hillert–Ohtani model, and the para-equilibrium grain boundary segregation, in which only carbon undergoes equilibrium segregation without diffusion of substitutional solute elements, was also discussed. The calculated results were correlated with the experimentally obtained Hall–Petch coefficients. To control the grain boundary segregation behavior, the solubility of carbon in ferrite was changed by altering the solution-treatment temperature, and the co-segregation of carbon steel with the addition of a third element, Mn or Si, was investigated in this study. As a result, good correspondence between the theoretically calculated values of grain boundary segregation and the experimental values of the Hall–Petch coefficient was confirmed for Fe-C and Fe-Mn-C alloys.

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 this study, changes in structure of sinter packed-bed during softening and melting processes were analyzed, and gas permeability of the cohesive layer was evaluated using X-ray CT images. First, the void structure of sinter packed-bed during softening and melting processes was visualized by X-ray CT images. In the softening process, the reducing gas flowed through the void between the sinter particles. In contrast, the reducing gas flowed through the generated melt phase in the melting process. Next, the changes in porosity and apparent particle diameter due to shrinkage of sinter layer were analyzed using CT images to evaluate the structural changes of sinter packed-bed during softening process. The porosity decreased with increasing the shrinkage of the sinter layer. In addition, the porosity tended to be smaller in the upper layer. The apparent particle diameter increased with increasing the shrinkage of the sinter layer. This is attributed to the deformation and the fusion of the sinter particles. Finally, the pressure drop of the sinter layer was calculated based on the Ergun equation using the porosity and the apparent particle diameter obtained from the CT images. As a result, the change in pressure drop was able to be well expressed up to a shrinkage degree of 0.5. The pressure drop was higher in the upper part of the sinter layer, suggesting that the pressure drop could be reduced by suppressing local blockage of the packed-bed.

It has been reported that an increasing H₂ gas ratio of the reducing gas in the blast furnace promotes the low temperature reduction disintegration of the iron ore pellet. Reduction of the pellet sample proceeds uniformly under higher H₂ condition at 500°C. Microcracks with the size of several micrometer form at the primary particles of iron oxide and it promote fine particles formation after the drum test. Macrocracks with the size of several millimeter form inside of the pellet after reduction and it promotes the volumetric destruction. In this study, the temperature dependence of reduction disintegration of self-fluxing pellet under higher H₂ condition was examined.

Pellet sample was reduced under CO and CO-H₂ gas conditions at 600°C and 700°C. After reduction, the disintegration test was conducted using the drum. Under higher H₂ condition at 600°C, the density of microcracks decreases with increasing reduction degree and it leads to lower of the RDI value than that at 500°C. The reason is that the volumetric expansion by the reduction from hematite to magnetite at 600°C is not significant compared with that at 500°C. The difference of reduction degree at the center and near the surface of the pellet increases with increasing the reduction temperature. Reduction reaction proceeds more topochemically by increasing reduction temperature and the addition of hydrogen. This change leads the macrocrack formation, which is same mechanism under CO gas condition at 500°C. At 700°C, on the other hand, this microcrack was not observed because the volumetric expansion by the reduction is lower than that at lower temperature. Therefore, the effect of hydrogen addition on disintegration is not significant at 700°C.

To explore smelting behavior of lump ores under hydrogen-rich conditions and guide optimization of burden structure of blast furnace after hydrogen injection, this study investigates the reduction and softening-melting behavior of lump ores. The results indicated that, compared to a pure CO atmosphere, the reduction properties of lump ore were significantly improved under a pure H₂ atmosphere, with the endpoint reduction degree reaching as high as 99%. The volume shrinkage of most lump ores increased after hydrogen enrichment. Notably, the shrinkage ratio of limonite before softening was considerably higher than that of hematite under both CO-N₂ and CO-H₂ -N₂ atmospheres. This suggests that the high-temperature compressive strength of limonite is lower than that of hematite. Hydrogen enrichment also led to a decrease in the softening beginning temperature of the lump ores, resulting in a broader softening range that shifted to a lower temperature range. The softening beginning and finishing temperatures of limonite were lower than those of hematite. Furthermore, hydrogen enrichment increased the melting beginning temperature, narrowed the melting range, and shifted it to a higher temperature region, thereby significantly improving the gas permeability of the burden column. After hydrogen enrichment, both the maximum pressure drop and permeability index of the lump ore decreased, which facilitated the reduction of the lump ore and the carburization of solid iron, ultimately increasing the mass of the dripping. These findings suggest that hydrogen enrichment can enhance the gas permeability of the burden column, thereby benefiting advanced smelting processes.

The friction-type joints using high-strength bolts are frequently employed for the assembly of structural steel components. The drawback of the combination of the friction-type joints and hot-dip galvanized steel plates for highly corrosive environments is the low slip coefficient at the friction interface in the as-coated condition. To increase the slip coefficient, labor-intensive blast processing or phosphate treatment is applied to the surface of the galvanized steel plates before assembly. In this study, we investigated the slip mechanism at the friction interface between as-galvanized steel plates through slip resistance tests on high-strength bolted friction joints, in hope of determining effective methods for overcoming the low slip coefficient in the as-coated condition. In the as-galvanized material, both the outermost Zn- and ζ(FeZn₁₃)-phase layers exhibit c-axis texture. Since the easiest basal (dislocation) slip plane for the Zn phase with the hexagonal close-packed structure is parallel to the friction interface, the Zn phase is geometrically prone to plastic deformation due to the shear stress applied on the friction interface. The evidence that the coarse-grained Zn phase was refined to small crystal grains upon macroscopic slippage at the friction interface indicated that the low slip coefficient was attributed to the readily deformable nature of the outmost Zn phase. Potential strategies for increasing the slip coefficient without pre-surface treatment include strengthening the soft Zn phase through grain refinement or texture modification, or complete removal of the Zn phase during galvanizing.

For decreasing carbon dioxide emission from iron- and steelmaking industry, hydrogen utilization in the blast furnace has been considered. Iron ore sinter is one of the major iron sources for the blast furnace. It is known that the effects of the hydrogen concentration in the reducing gas on the reducibility and reduction disintegration of the sinter are strong. In this study, the evaluation of the mineral phase of the Mosaic EmBedding Iron Ore Sintering (MEBIOS) sinter and reducibility using a laboratory scale furnace simulated the blast furnace condition with high hydrogen concentration and the experimental blast furnace were carried out.

MEBIOS sinter has higher ratio of the mineral phases, i.e., hematite and acicular calcium ferrite with primary hematite, showing higher reducibility compared to the conventional sinters. The value of JIS-RDI of the MEBIOS sinter decreases with an increase in that of JIS-RI, which is the reverse trend of the conventional sinter. Further, the basket charge test with the experimental blast furnace confirmed that the MEBIOS sinter shows high reducibility under the condition of high hydrogen concentration while the reduction disintegration behavior at low temperature is similar to conventional sinter.

Hydrogen utilization in a direct reduction shaft furnace is a promising technology for carbon neutrality. On the other hand, some kind of heat compensation appears to be necessary, because the temperature in the furnace decreases and the reduction degree stagnates due to hydrogen enrichment. Therefore, a tool which can quantitatively evaluate the efficiency of heat compensation from a kinetic viewpoint considering detailed heat and mass transfer is useful for operational design. Based on the above, a numerical simulation model based on DEM-CFD was developed for the direct reduction process, and the following findings were obtained.

(1) A numerical analysis simulating a model plant confirmed that the calculation accuracy of the developed model is sufficiently high. The gas composition varies greatly depending on the degree of achievement of shift equilibrium.

(2) A numerical analysis of a commercial plant revealed the distribution with low temperature and low reduction degree in the radial center of the furnace. Hydrogen enrichment lowers the temperature and expands the region with a low reduction degree.

(3) As a technique for thermal compensation for hydrogen enrichment, it was found that increasing the inlet gas temperature increases the reduction degree exponentially.

(4) DEM-CFD can be a useful approach, since operational design considering powder phenomena , as represented by reduction degradation and clustering, appears to be necessary.

In the steelmaking industry, the utilization of CO₂ as a resource has become one of the important research projects. The decarburization and desilication mechanism were investigated to the extension range of low carbon condition and in Fe-C-Si ternary system in 1873K. ¹³CO₂ and ¹⁸O₂ dual isotope gases were use to clarify the complicated oxidation process. The results showed that in Fe-1.0 mass%C-0.5 mass%Si molten alloy, CO₂ substitution part of O₂ within 40% slightly reduced the decarburization rates in the advantage area of decarburization, and after reaching the oxidation equilibrium curve, the decarburization rates were basically stable and low even 100% CO₂. However, with introducing CO₂ from 0 to 40%, the desilication rates were dropped a lot. CO₂ replacing part of O₂ was beneficial to reducing the loss of silicon during decarburization process at 1873 K. The critical value of carbon content was around 0.3 mass%, that the main limiting rate step was transformed to the diffusion of carbon in molten under the correspondindg condition of 1.2 to 3.2 Nm³/t·min gas supply intensity in the present experiments. When the gas supply was sufficient, CO₂ participation ratio was decreased and that of O₂ was increased with the carbon content decreasing. When the gas supply was insufficient, both CO₂ and O₂ participation ratios were relatively stable until the carbon transfer limiting the reactions.

To improve the stability of hydrogen-enriched reduction operations in blast furnaces, it is necessary to maintain gas permeability in the cohesive zone. The reduced and produced metallic iron phases contribute to the strength of the iron ore in the cohesive zone. However, the form of the iron produced and its evaluation method have not been established. In this study, sinters, pellets, and lump ores were reduced, and the iron phase produced was evaluated using a local thickness measurement method. The effects of the reduction conditions and the composition of the iron ore on the local thickness profiles of the iron structures in the ore were discussed.

Currently, the Japanese steel industry is developing the technologies to reduce 30% of domestic CO₂ emissions from iron- and steelmaking industry using an innovative ironmaking process such as the COURSE50 project, which focuses on H₂ reduction and CCUS technologies. On the other hand, it has been reported that an increasing H₂ gas ratio in the blast furnace reducing gas promotes the low temperature reduction disintegration of the iron ore pellet. In this study, the low temperature reduction disintegration mechanism of self-fluxing pellet under higher hydrogen condition at 500°C was examined. During hydrogen reduction which proceeds uniformly, the fine cracks with few micrometers in the primary particles form. It leads to the formation of fine particles with the size of less than 0.1 mm on the surface of the pellet. Increase in the particles with few millimeters makes a significant impact on the permeability of the blast furnace. On the other hand, CO reduction without hydrogen gas proceeds topochemically, and volumetric fracture progresses with generation of the cracks with several millimeters in length due to the stress difference between near the surface and in the center of pellet. Under higher H₂ conditions, reduction proceeds uniformly, so such cracks causing volume fractures are hard to form, but the finer cracks are easier formed than the case of CO reduction, and the amounts of finer particles increases.

This study introduces a new convergence simulation procedure for representing the softening–melting behavior of reduced sinter at a higher resolution in the cohesive zone by incorporating the inner structure obtained by X-ray computed tomography. Boundary conditions for the actual sinter shape, including internal voids, were integrated into a dynamic calculation scheme. The composition distribution inside, corresponding to the total reduction degree, was computed by applying a three-dimensional reaction–diffusion model, and the core–shell structure within the ore was modeled as two distinct phases based on the local reduction degree. The Bingham fluid model was applied to track the fluidic behavior of the softened sinter, and an elastic force term was added to the reduced iron shell to represent its hardness. The stiffness parameter in this model was optimized by comparing the softening–melting behavior of single sinter particles across different overall reduction degrees when held at temperatures of 1573–1673 K under load. Additionally, we present an example calculation using a packed bed deformation model that extends the single sinter softening deformation model. This study confirmed the ability to evaluate the softening deformation behavior and accompanying structural changes of individual sinter particles. This series of procedures is useful for understanding the deformation behavior of mixed iron ore types in a packed bed from both micro and macro perspectives and could serve as a powerful method for designing rigorous operations for ultra-low carbon emission operations.

This study extended a dynamic model of the softening and melting behavior of sinter in the cohesive zone of a blast furnace to clarify the deformation behavior of a packed bed in relation to the internal morphology of a two-layer structure. This structure comprises a solid–liquid coexisting oxide phase (core) and porous iron (shell), with internal voids in the sinter particles that change owing to gas reduction. The detailed morphology of the sinter was obtained through industrial X-ray computed tomography (CT), and the structural changes and permeability of the packed bed were estimated through gas flow analysis. The results demonstrated that changes in the internal structure led to increased shrinkage as the degree of reduction and shell elastic force decreased. Even when the rotational and translational motions of the sinter particles were excluded, significant linear deformation was observed in the horizontal and vertical directions, and 3D behavior occurred on a particle-by-particle basis. Permeability analysis quantified the pressure changes resulting from ore deformation and the resulting core outflow. The results revealed that gas flow channels narrowed and were blocked as the reduction rate and shell elasticity decreased. The advantage of this newly proposed procedure is its extension of convergence engineering simulation technology. This is valuable for further understanding the chemical and physical heterogeneity of ore particles in packed beds based on actual measurements.

Strain-induced lattice defects that form during the incubation stage of hydrogen embrittlement fracture in the plastic region were quantified and their relationship with mechanical properties and fracture morphologies was investigated. Pure iron was subjected to plastic strain by tensile testing at various strain rates and hydrogen charging conditions. After charging tracer hydrogen as a probe for detecting lattice defects under conditions that reached equilibrium, specimens were quickly cooled with liquid nitrogen to prevent hydrogen desorption, and total tracer hydrogen was detected using low-temperature thermal desorption spectroscopy (L-TDS), which is capable of continuously elevating the temperature and subsequently performing measurement from that temperature. Dislocation density was not affected by the strain rate or hydrogen content. However, the vacancy concentration increased in the presence of hydrogen and displayed strain rate dependence even at the same strain level. A comparison of the mechanical properties with/without hydrogen showed that the flow stress with hydrogen increased with a decreasing strain rate compared with that without hydrogen, i.e., dislocation mobility decreased. It was established that strain-induced vacancies, which were excessively generated in the presence of hydrogen and formed complexes with it, were responsible for reducing dislocation mobility. Furthermore, fractures, albeit predominantly quasi-cleavage ones, along the {001} plane, which is the cleavage plane in body centered cubic iron, were present on the fracture surfaces, and their proportion increased with decreasing dislocation mobility. This suggests that vacancy-hydrogen complexes contribute to cleavage fracture by inhibiting dislocation motion.

Introducing hydrogen gas into the blast furnace to partially substitute pulverised coal or coke, is a promising solution to decrease CO₂ emissions of ironmaking process. However, increased H₂O concentration alters the thermal and chemical conditions in the furnace, impacting the gasification reaction rate and degradation mechanism of coke. This research developed a modified random pore model (RPM) to integrate internal diffusion and interfacial chemical reaction processes, aiming to study reaction mechanisms and structural changes in coke under simulated conventional and H₂-enriched blast furnace conditions. High-temperature thermogravimetric analysis was used to evaluate the gasification of coke lumps with varying initial quality. The experiments were performed isothermally between 1173-1473 K. Results indicated that coke reactivity in an H₂-rich environment is up to 1.5 times higher than the conventional case. Moreover, low CRI coke exhibited a lower reaction rate in the H₂-rich case, indicating the importance of coke quality for modified blast furnace operations. Modelling results showed that in the conventional blast furnace case, reactions occur more uniformly across the coke radius, indicating that chemical reaction is the dominant mechanism. In contrast, in the H₂-rich blast furnace case, gas diffusion becomes the dominant rate limiting factor at higher temperatures (i.e., 1473 K), leading to higher mass loss near the coke surface and leaving a less-reacted core. These effects are more pronounced in low CRI coke due to its lower diffusivity coefficient. The results suggest that low CRI coke in an H₂-rich blast furnace helps minimise coke degradation and maintain structural integrity.

The efficiency of blast furnaces is adversely affected by coke degradation via gasification. Considering the utilization of hydrogen-enriched blast furnaces, it is essential to investigate the reaction and degradation behaviors of coke at different temperatures. In this study, coke gasification experiments were conducted under CO₂ and H₂O atmospheres at different temperatures to prepare cokes with a conversion ratio of 0.2. The reaction rate of the H₂O gasification reaction was higher than that of the CO₂ gasification reaction at the same temperature. The activation energies for CO₂ and H₂O gasification were 150.2 and 126.0 kJ/mol, respectively. After gasification, the shrinkage ratio was low by H₂O gasification at 1273 K and increased with increasing temperature, indicating that the surface reaction became the control factor that consumed the coke matrix with increasing temperature. On the other hand, the shrinkage ratio by CO₂ gasification tended to be stable from 1273 to 1673 K. Furthermore, the increase in the porosity of coke by H₂O gasification was lower than that by CO₂ gasification at higher temperatures. In addition, the strength of the coke via H₂O gasification was higher than that of the coke via CO₂ gasification.

Blast furnace blowing break and re-blowing is a regular operation in the smelting process, However, some blast furnace conditions fluctuate for a long time due to improper operation of blast furnace blowing break and re-blowing, and preventing rapid attainment of production capacity. This paper first analyzes the influence of hydrogen-rich on the cohesive zone. Subsequently, it simulates the conditions of ferrous burden during partial and complete tuyere blowing break under hydrogen-rich conditions, followed by re-blowing. The study explores the influence of these operational changes on the softening and melting behaviors of the ferrous burden. The results indicate that with a 10% hydrogen enrichment, the melting range of ferrous burden narrows and shifts to higher temperatures, improving the permeability of the burden. During partial tuyere blowing break, this promotes the reduction of the ferrous burden and the carburization of metallic iron, increasing the melting start temperature and decreasing the dropping temperature by 29°C, thereby narrowing the cohesive zone. Both maximum pressure difference (ΔP_max) and permeability index (S) values decrease. In contrast, with a complete tuyere blowing break, the dropping temperature of the ferrous burden gradually increases from 1459°C to 1478°C as the isothermal duration extends, widening the melting interval and leading to an increase in both ΔP_max and S values.

Gas permeability in a blast furnace is maintained via a layered structure comprising iron ore and a coke bed. High temperatures may induce a breakdown of this layered structure, and hence, an understanding of the transition from solid-like deformation to liquid-like deformation is crucial for preventing the breakdown. In this study, the flow behavior analogous to that of a layered structure comprising iron ore and a coke bed with derived melts was examined using polyethylene beads and silicone oil. Oscillation and creep tests were conducted on analogous samples of polyethylene beads and silicone oil with viscosities similar to that of the slag melt. The samples were prepared by mixing at liquid-phase to solid-phase volume ratios of 10/90, 25/75, and 40/60. Air was present in the samples used herein. The transition between the solid-like and liquid-like flow was investigated via oscillation testing, and the flow behavior on long timescales was investigated via creep testing. The results of oscillation testing indicated that a larger strain is required for flow at an intermediate liquid fraction or greater liquid viscosity. The results of creep testing revealed that the sample deformation changes from decelerating to accelerating as the applied stress increases at higher or lower liquid-phase fractions. In contrast, at an intermediate liquid fraction, the sample deformation decelerated at a relatively higher stress. The number of liquid bridges may be the highest at an intermediate liquid fraction, and the force between the particles generated by the liquid bridges is expected to be the most significant.

Knowledge of the viscoelastic properties of suspensions is essential for many industrial processes. Although oscillation and creep testing are widely used to measure the viscoelastic properties of complex fluids, few studies on the correlation between the viscoelastic properties measured using these methods have been published. This study aims to provide insights into the differences between these methods and determine which method is better suited for a particular application. The room-temperature viscoelastic properties of a suspension composed of polyethylene beads dispersed in a silicone oil matrix were measured by oscillation and creep testing and compared. The results of oscillation testing indicated that the suspension showed weakly elastic deformation, whereas the results of creep testing revealed that the suspension was relatively elastic, with the liquid phase showing lower viscosity. In addition, the viscosity measured by oscillation testing was lower than that measured by creep testing. When the imposed flow causes microstructural changes, such as when the shear flow and particle‒particle contact induce aggregation, the analyzed flow property considerably differs between testing methods.