To improve the quality of steel production, it is important to understand the behavior of bubbles rising in a liquid metal under a horizontal magnetic field (MF). However, such behavior has not been fully experimentally evaluated because of the limitations of existing experimental methods. In this study, a two cross-sectional ultrasonic tomography (UT) method was developed and used to measure the 3D motion of bubbles in a cylindrical container with an inner diameter of 50 mm. We conducted UT measurements alternately at the upper and lower measurement cross-sections of the container using the developed method, with a measurement interval of 2 ms in each cross-section. The applicability of this system was evaluated by measuring the 3D behavior of bubbles in a gallium alloy under different MF strengths. When no MF was applied or the MF strength was lower, the directions of the velocity vectors were randomly distributed. However, they aligned in the direction of the flow channel with an increase in the MF strength. With an increase in the flow rate, that is, as the distance between the bubbles decreased, the velocity oscillations of the bubbles perpendicular to the MF direction were greater than those parallel to the MF direction at higher MF strengths. Consequently, the distribution of the bubble-passing positions at the cross-section was slightly more spread in the direction perpendicular to the MF than in the parallel direction. These results demonstrate the effectiveness of the developed method in evaluating the 3D behavior of rising bubbles in a liquid metal.

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.

Fatigue tests under axial loading were conducted on steel with a shallow hardened layer induced by induction hardening, and in situ X-ray stress measurements were performed to investigate the relaxation of residual stresses during fatigue. The residual stresses were relaxed owing to tensile loading and not compressive loading. The two conditions that bring about this phenomenon are (i) a high peak of tensile residual stress just below the hardened layer, and (ii) the hardened layer coinciding with the compressive residual stress field that prevents the yielding of the compressive residual stress field under compressive loading. In this case, tensile yielding occurred just below the hardened layer under tensile loading, the residual stresses are redistributed, and the compressive residual stress on the material surface is relaxed. The experimental results also showed that the fatigue fracture morphology changed depending on the residual stress relaxation behavior.

Microstructures of lath martensite have been studied intensively to understand their effect on the mechanical properties of steels. It is, however, said that the relation between microstructural factors and mechanical properties has not been clarified yet. The plastic deformation behavior of fully lath martensitic steels has become important because they are applied to automobile body structures such as bumper reinforcement. It is, therefore, important to understand the microstructural factors that control the work-hardening behavior of fully martensitic steels. Although we could not clarify differences in microstructural factors when manganese (Mn) concentrations of steels are altered, the work-hardening of 8 mass%Mn martensitic steel is much higher than that of 5 mass%Mn martensitic steel. It was found using the digital image correlation (DIC) method, that the strain concentration due to the in-lath-plane slip deformation is more developed in 5 mass%Mn martensitic steel than 8 mass%Mn martensitic steel. Transmission electron microscope (TEM) observations revealed the existence of two types of fine twins inside laths. Long twins that are parallel to the longitude of the lath are observed both in 5 mass%Mn and 8 mass%Mn martensitic steels. Short twins that partially cross the laths, on the other hand, can only be found in 8 mass%Mn martensitic steel. Since twin boundaries are high angle boundaries, the short twins are supposed to prevent the development of in-lath-plane slip deformation. This seems to be the mechanism of higher work-hardening behavior observed in 8 mass%Mn martensitic steel.

Stress and plastic strain distributions and those partitioning behaviors of ferrite and retained austenite were investigated in the medium manganese (Mn) and the transformation-induced plasticity-aided bainitic ferrite (TBF) steels, and the martensitic transformation behaviors of retained austenite during Lüders elongation and work hardening were analyzed using synchrotron X-ray diffraction at SPring-8. The stress and plastic strain of retained austenite and volume fraction of retained austenite were remarkably changed during Lüders deformation in the medium Mn steel, implying that the medium Mn steel possessed inhomogeneous deformation at the parallel part of the tensile specimen. On the other hand, the distributions of the stress, plastic strain and volume fraction of retained austenite were homogeneous and the homogeneous deformation occurred at the parallel part of the tensile specimen at the plastic deformation regime with work hardening in the medium Mn and TBF steels. The martensitic transformation of retained austenite at Lüders deformation in the medium Mn steel was possessed owing to the application of high stress and preferential deformation at retained austenite, resulting in a significant increase in the plastic deformation and reduction of stress in the retained austenite. The martensitic transformation of retained austenite at the plastic deformation regime with work hardening was induced by the high dislocation density and newly applied plastic deformation in retained austenite in the medium Mn steel whereas the TBF steel possessed gradual transformation of retained austenite which is applied high tensile stress and moderate plastic deformation.

Depending on the operational conditions inside a direct reduction shaft furnace, e.g., ingoing gas temperature, feeding rate of material, and gas composition, the outgoing material will differ. This study investigates how the heating rate affects the reduction during pure hydrogen reduction of commercial iron ore pellets. As expected, the reduction rate increased with increasing heating rate. The heating rate also significantly affected the microstructure evolution inside the pellet. Inside the hydrogen direct reduced pellets, the iron had two appearances: (1) porous iron containing small and numerous intragranular pores, or (2) dense iron with larger but fewer intragranular pores. The pellet reduced with the slowest heating rate consisted of only porous iron, while the faster heating rates comprised porous and dense iron. The amount of dense iron gradually increased with increasing heating rate and was found to start forming at a temperature of around 668 °C. The solid iron aggravated the mass transfer through the product layer and decreased the total reaction rate. This led to an expanded spread of the reaction zone as the heating rate increased. Through this work, it was also shown that insignificant reduction took place below a temperature of 450 °C. Lastly, the microstructure that evolved during the non-isothermal reduction vastly differs from the microstructure formed during isothermal reduction. Consequently, an effective diffusivity and thermal conductivity that varies with time and temperature must be considered when optimizing the shaft furnace reactor.

The preparation of glass microbeads by gas quenching of blast furnace slag is an effective way to achieve efficient recovery and resource utilization of the residual heat from blast furnace slag. However, due to the high viscosity and easy crystallization of blast furnace slag, there are problems such as low bead formation rate, opaque glass microbeads, and poor chemical stability. MnO tempering agent was developed, and the influence of MnO on the crystallization behavior and rheological properties of the tempered slag was analyzed. The evolution law of the crystallization phase of the tempered slag was clarified, and a viscosity-crystallization coupling control method conducive to the bead formation of blast furnace slag was proposed. The results show that during the isothermal process, when the MnO content in the tempered slag is in the range of 0.17 - 12.24%, with the increase of its content, the initial crystallization temperature and the amount of crystal precipitation gradually decrease, effectively inhibiting the precipitation of crystals. However, when the MnO content exceeds 12.24%, the excessive MnO increases the activity of the easily precipitated phase, and the initial crystallization temperature increases instead. Therefore, when the MnO content in the tempered slag is 12.24%, the crystallization ability is the weakest, and the glass phase content is the highest. In the continuous cooling process, when the MnO content in the tempered slag is 12.24% and the cooling rate exceeds 3 °C/s, the tempered slag completely solidifies into a glassy state.

Addressing the threat of global climate change is an urgent priority for all industries. The Paris Agreement set the global long-term goal of carbon neutral by 2050 for all member countries. As the steel industry occupies approximately 7.2 % of the total global greenhouse-gas emissions, innovative technologies that build upon or move beyond the past developments are desired to reach this long-term goal. Various zero carbon technologies have been proposed for the steel industry. This review focuses on the current state of the steel industry from the perspective of long-term targets and pathways for the future. The design of an optimal ironmaking process for low carbon and decarbonization is discussed from a technological perspective, considering comprehensive consistency with sustainability in the steel industry. In particular, perspectives on the hydrogen-based ironmaking process using renewable energy for carbon direct avoidance and smart carbon usage are described.

Wettability between molten iron and non-metallic inclusions is an important factor, as it influences the behavior of non-metallic inclusions during secondary metallurgy. In the present study, the wettability of CaS against molten iron was investigated using the sessile drop method at 1873 K. The CaS substrate was fabricated using spark plasma sintering, achieving a high relative density of 98%. The measured contact angle of CaS against molten iron was found to be 118 degrees. This finding indicates that the wettability of CaS is poor, which contrasts with the previous report. This result will contribute to further understanding regarding the inclusions' behavior during secondary refining processes.

Titanium-bearing blast furnace slag (TBFS), a byproduct of ironmaking processes, has long been discarded as waste, resulting in the squandering of valuable resources such as titanium. The recovery and effective utilization of TBFS hold immense significance and importance. This study reports a direct electrolysis method for synthesizing Ti₅Si₃ alloy from a TBFS/SiO₂ mixture in molten CaCl₂ at 950 °C. A comprehensive investigation was conducted into the phase and morphological evolution during the electrolysis process, along with an analysis of the migration behavior of impurities such as Ca and Al present in TBFS. The synthesized Ti₅Si₃ alloy powder was systematically characterized and analyzed using scanning electron microscopy, transmission electron microscopy, and other techniques. The results reveal that the electrolysis process encompasses electrochemical deoxidation, in-situ alloying, and self-purification. Furthermore, this study achieved further purification of the Ti₅Si₃ alloy through vacuum laser rapid melting, effectively volatilizing and removing the residual impurity elements, resulting in an increase in the purity of Ti₅Si₃ alloy from 96.8% to 98.6%. The resultant Ti₅Si₃ alloy exhibits excellent corrosion resistance in phosphate buffer solution. In summary, this work provides a crucial technical paradigm and scientific theoretical foundation for the resourceful and value-added utilization of ironmaking solid waste, specifically TBFS.

Lubrication is critical to achieve stable rolling during the cold rolling of flat steel products. However, the oil film thickness distribution in the roll bite and its effect on the friction between the work roll and strip has not yet been clarified. This study aims to elucidate the relationship between the oil film thickness distribution and friction by focusing on the rolling oil viscosity and steel grades because they significantly affect the friction between the work roll and the strip. Rolling oil was prepared with quantum dots (QDs) as the fluorescent additive and used in rolling experiments to determine its distribution. Furthermore, cold rolling experiments were conducted using two types of oils with different viscosities and three steel grades: low-carbon steel (LCS), high-strength steel (HSS), and advanced high-strength steel (AHSS) with tensile strengths of 270, 590, and 1180 MPa, respectively. Subsequently, the oil film thickness distribution on the steel strip surface was visualized by fluorescence microscopy using QDs. The idea that the higher the tensile strength of the steel or the higher the oil viscosity, the wider the rolling oil distribution on the strip surface was demonstrated. The numerical analyses revealed that the rolling oil distribution on the steel sheet surface was wider for AHSS and HSS than that for LCS. The high surface pressure between the roll and the steel plate may have increased the oil leaching area by increasing the oil viscosity. These findings demonstrate that rolling oil permeation from oil pits reduces the friction between the work rolls and the strip.

The high temperature oxidation behavior of the electroslag remelting (ESR) process of welded 30CiNiMo8 billets electrode is investigated. High-temperature oxidation experiments are conducted to clarify the scale formation kinetics for the model. The steel is heated at 700-1200 °C under a 21% oxygen atmosphere. The oxidation kinetics of the steel follow a parabolic law, with the oxidation rate equilibrium constant lnK=-23.801×1/T+17.866 and apparent activation energy ΔE_a=197.88 J/mol. The temperature distribution on the electrode surface is obtained by measurement and fitted vertically and horizontally. The temperature increases exponentially with the electrode height, and the temperatures on the surface cross-section are inconsistent. Finally, the oxidation weight gain model is established by applying the isothermal oxidation kinetics model, the Arrhenius equation, and the Simpson formula. The amount of FeO_x carried into the slag under the industry experiment is 58.68 mg/s with the content of FeO as 65 wt%, which is established by the EDS and EBSD of the scale, and 4.77 g of aluminum addition into the slag pool every 5 minutes is suggested to reduce the FeOx potential when using four 160×160 mm welded billets electrode with a descending speed as 1.19×10^-4 m/s.

The ironmaking industry consumes significant fossil fuel-derived carbon as a heat source, reducing agent for iron ores, and carburizing agent for reduced iron. Despite the demand for reduction of carbon dioxide emission, carbon is essential for smelting molten iron. A carbon recycling ironmaking process using circulating CO has been proposed to achieve carbon neutrality. However, this process does not consider molten hot metal production because CO does not dissolve sufficient carbon in iron to be melt. Our group has suggested a new carbon recycling ironmaking process capable of producing hot metal. This process utilizes free carbon and iron carbides produced via carbon deposition reactions using metallic iron as a catalyst. CO gas produces only Fe₃C, whereas adding H₂ gas also produces Fe₅C₂. The composite, agglomerated with these carbonaceous materials and fine iron ore (Deposited Carbon-Iron Oxide Composite: DCIC), is reduced and melted in a furnace. This study focuses on the effects of iron carbides and free carbon on the melting behavior of DCIC.

A rolling force prediction method based on transfer learning and Inception-LSTM neural network is proposed to address the problem of low efficiency in predicting rolling forces for individual rolling mill stands due to the complex rolling conditions and distribution differences in the collected process data. The Inception-LSTM neural network combines the spatial feature extraction of the Inception model and the time sequence modeling capability of the LSTM network to comprehensively capture the features in the rolling process, thus establishing a baseline prediction model. Then, the transfer learning method is employed to transfer part of the parameters and structure of the baseline prediction model to the new prediction model. Simultaneously, the model is fine-tuned to establish a new transferred model for rolling force prediction, which is compared and analyzed against the neural network prediction model without using transfer learning. Experimental results show that the model built with transfer learning is higher fitting accuracy than the model built directly for rolling force prediction, and the training time of the model is significantly reduced. It can be used for steel shape and thickness control and digital twin simulation of rolling process.

The high aluminum concentration in advanced high-strength steels lowers the oxygen activity at the steel-slag interface, compared with conventional low-carbon aluminum-killed steels. The lower oxygen activity affects the rate and equilibrium extent of steel-slag reactions. One result of the lower oxygen activity is a higher concentration of dissolved magnesium, leading to faster conversion of alumina inclusions to spinel inclusions, and spinel to periclase – as demonstrated in previous work. The current study concerns the dissolution of nitrogen in ladle slag as nitride ions. Laboratory results of the rate and extent of nitrogen removal are compared with model predictions, confirming that substantial nitrogen removal is possible. While aluminum nitride was found in some steel samples after solidification, aluminum nitride does not appear to play a role in nitrogen removal from liquid steel to liquid slag.

During two stage cold rolling, texture and formability at various reduction distribution coefficients (n) were investigated for ferritic stainless steel for elucidating the evolution of recrystallization texture and leveraging the advantages of this process. The shear band-induced crystallite occurred during cold rolling, and a model of crystallite-assisted γ-fiber texture development was presented during annealing. High cold rolling reduction promoted the crystallite formation and their transformation into more stable {111}<112> components, and the {111}<112> recrystallized nuclei growth, while low cold rolling reduction retarded the phenomenon that the surrounding matrix of deformed grain occurring preferential nucleation was consumed through priority developed γ-fiber recrystallized grain, and promoted the {111}<110> recrystallized nuclei growth during final annealing. Hence, after final annealing, as n decreased (first and second stage cold rolling reductions increased and decreased, respectively), the γ-fiber textures weakened and the fluctuation of intensity along γ-fiber reduced, and the intensity of {110}<001> component displayed a gradual increase followed by reduce. Moreover, as n decreased, the distribution for oriented grain clusters after annealing exhibited gradual uniformity followed by unevenness on account of low degree of microstructure fragmentation and high recovery tendency at lower cold rolling reduction and high nucleation and growth tendency of grains with similar orientations at higher cold rolling reduction. As n decreased, therefore, the ridging resistance and anisotropy of r-value displayed a step-by-step rise followed by a step-by-step reduce, and the difference in r-value was small. The n of 0.405 contributed to realizing optimal matching of r-value and its anisotropy and ridging resistance.

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.

This study identifies a method for shortening the duration of annealing in the grain boundary control process to achieve a high frequency of CSL boundaries in austenitic stainless steel by focusing on decreasing stacking fault energy. Si-added SUSXM15J1, which has significantly lower stacking fault energy, was used to examine the impact of a decreased stacking fault energy on the duration of annealing after cold-rolling, necessary to introduce a high frequency of CSL boundaries, by comparing it with SUS304 austenitic stainless steel. It was found that a decrease in stacking fault energy significantly contributed to shortening annealing duration. The frequency of the CSL boundaries in SUSXM15J1 increased from 55% to 75% through 5% cold rolling and subsequent annealing at 1323 K for only 60 s. Ex-situ and in-situ EBSD observations revealed that the strain-induced grain boundary migration, accompanied by the formation of twin boundaries, likely occurred in SUSXM15J1 compared to SUS304, as the recovery process was hindered by the lower stacking fault energy resulting from Si addition.

During resistance spot welding of zinc-coated advanced high-strength steels (AHSS), cracks which are promoted by liquid metal embrittlement (LME) may occur. According to previous researches, welding current, welding time, electrode tip diameter and electrode misalignment angle are significant factors on LME cracking. In this study, the effects of these four factors on LME cracking were compared with an orthogonal design experiment. After welding, numbers and lengths of cracks were measured, and Crack Index (CI) of each experiment group was calculated for comparison. As the result, two types of LME cracks, i.e., Type A cracks located at the indentation of electrode tip and Type B cracks located at the indentation of electrode shoulder were observed. The order of influence degree on CI of Type A crack from high to low was welding current > electrode tip diameter > electrode misalignment angle > welding time. The order of influence degree on CI of Type B crack was electrode tip diameter > electrode misalignment angle > welding time > welding current. The result reveals that modifying welding current is the most effective way to reduce Type A cracks and optimizing the electrode tip diameter is significant for preventing Type B cracks.

The thermophysical properties of molten Fe–Cu alloys, including density, surface tension, and viscosity, were measured using the electrostatic levitation furnace aboard the International Space Station (ISS-ELF) under microgravity conditions, which provided an environment that facilitated accurate measurements. The densities of the molten Fe–25at%Cu and Fe–50at%Cu alloys decreased linearly with increasing temperature, and higher copper compositions resulted in increased density. The surface tension of the molten alloys exhibited a unique up-convex temperature dependence curve that initially increased and then decreased as the temperature increased. Viscosity measurements indicated that the viscosity of the molten Fe–Cu alloys decreased with increasing temperature, following a quadratic curve, and that an increase in the copper composition resulted in lower viscosity.

Handling dephosphorized iron-ore powders with varying sizes and degrees of reduction is a pivotal issue in the iron-making process. A wet granulation process is employed for using dephosphorised fine ore powders as raw materials; however, it is difficult to determine the optimum water content to produce green pellets with the required physical properties because of the significant variation in the physicochemical properties of the dephosphorized ore powders. Thus, developing a method to determine the optimum water content for producing green pellets from fine ore powders with various degrees of reduction is necessary. In this study, we propose a method to estimate the optimum water content using agitation torque, which is a rheological property of wet ore powders. To this end, we investigated the effects of the hematite/magnetite fraction in the raw ore powder mixture on the agitation torque and green pellet properties. The characteristics of the agitation torque profile and green pellet properties (density and compressive strength) changed significantly depending on the hematite/magnetite fraction. Subsequently, we investigated the relationship between the agitation torque and green pellet properties, which revealed that the density and compressive strength of the green pellets correlated well when the product of the agitation torque and tumbling time was employed as the explanatory variable, regardless of the hematite/magnetite fraction. Thus, the properties of green pellets produced from fine ore powders with various degrees of reduction can be estimated based on the rheological properties measured by the agitation torque.

In drawn pearlitic steel wire, hydrogen embrittlement cracks are preferentially formed along cementite / ferrite interfaces perpendicular to the tensile stress, predicting an anisotropy in the hydrogen embrittlement resistance of the wire. To validate this prediction, notched miniature tensile tests specimens were extracted from the wire with their orientation changed, and in-situ miniature tensile tests were conducted during plasma hydrogen charging in a scanning electron microscope. The fracture process was also investigated from secondary electron images simultaneously obtained during these in-situ miniature tensile tests. As a result, it was revealed that, in accordance with the prediction, the fracture stress is decreased by the plasma hydrogen charging for the specimens with the tensile direction perpendicular to the drawing direction of the wire whereas it is hardly changed for the specimen with the tensile direction parallel to the drawing direction. In the secondary electron images, a stationary subcrack was observed before the fracture only for the specimen with the tensile direction parallel to the drawing direction. Based on finite element method analysis results, the subcrack was found to be formed by the triaxial stress due to the notch. The difference in the presence and absence of the subcrack depending on the specimen orientation was also well explained from the preferential hydrogen embrittlement crack formation along the cementite / ferrite interfaces perpendicular to the tensile stress.

In this study, the solidification path and crack sensitivity of high‑manganese austenitic cryogenic steel (HMACS) were studied based on DSC and directional solidification experiments. DSC experiment explored the solidification mode with the result that the solidus of the steel is 1342°C and the liquidus is 1400°C. Subsequently, the relationship between solid fraction and temperature of HMACS was analyzed by DSC and directional solidification experiment with a pulling velocity of 5μm/s. Based on this relationship, the brittleness temperature range of HMACS and its crack sensitivity were analyzed. The results suggest that the high crack sensitivity of HMACS is primarily due to its broad brittleness temperature range. Furthermore, according to the directional solidification experiments with different pulling velocities, the solidification cracks and microporosities of HMACS during the brittleness temperature range were also characterized and analyzed by using thermal stress calculations. All results express that the high crack sensitivity of HMACS is primarily due to its broad brittleness temperature range. This leads to the solidification structure experiencing a longer brittle period, resulting solidification cracks and microporosities defects during the liquid-to-solid transition.

During steel-manufacturing, molten slag is foamed through gas injection and gas generation reactions. However, molten iron droplets are trapped in the slag. The settling velocity of an iron droplet in the foaming slag is important because the residence time of an iron droplet in the slag is used to directly calculate the settling velocity. Previous studies have shown that the rate of settling velocity is lower than that observed in regular non-foaming slag. However, this has not been quantitatively determined. This study measured the settling velocities of particles through a foaming glycerin-water solution. A dimensionless correlation equation for particle settling velocity in the formed liquid was proposed by conducting a dimensional analysis of the experimental data. Using the obtained equation, the settling velocity of iron particles in the foaming slag was predicted. The settling velocity of iron particles was significantly affected by the volume fraction of the gas phase in the foaming slag. A threshold for the velocity was observed; the velocity of particles below this threshold was zero.

The identification of internal α-alumina (α-Al₂O₃) scales is crucial because α-Al₂O₃ determines the performance of heat-resistant alloys. A non-destructive method was recently developed to rapidly identify internal α-Al₂O₃ scales on the Ni–Cr–Al and Ni–Al alloys by obtaining their surface cathodoluminescence (CL) spectra. However, the peak intensities at 695 nm originating from α-Al₂O₃ considerably deviated from those estimated from the attenuation rates of overlaid scales (Cr₂O₃, NiO, and NiAl₂O₄) and the CL peak intensity at 695 nm for the α-Al₂O₃ scale on the Fe–Cr–Al alloy surface. In this study, factors causing the deviations in the CL peak intensity at 695 nm for the internal α-Al₂O₃ scales were investigated by obtaining images of the scales and their CL spectra. The surface Cr₂O₃ scale on the Ni–25Cr–5Al alloy exhibited a surface the roughness of ~1 μm, causing the CL peak intensity at 695 nm to be one order of magnitude higher than the estimated value. The CL spectrum and scanning transmission electron microscopy observation revealed that θ-Al₂O₃ overlaid on α-Al₂O₃ in the internal Al₂O₃ scale on the Ni–14Al alloy reduced the CL peak intensity at 695 nm by two orders of magnitude.

The surface defect of hot-rolled strip is a significant factor that impacts the performance of strip products. In recent years, convolutional neural networks (CNNs) have been extensively used in strip surface defect recognition to ensure product quality. However, the existing CNNs-based methods confront the challenges of high complexity, difficult deployment and slow inference speed. Accordingly, this work proposes a soft optimization knowledge distillation (SOKD) scheme to distill the ResNet-152 large model and extract a compact strip surface recognition model. The SOKD scheme utilizes Kullback-Leibler (KL) divergence to minimize the error between the soft probability distributions of the student network and the teacher network, and gradually reduces the weight of "Hard loss" during the training process. The operation significantly reduces the learning constraints that the prior knowledge of the teacher network on the student network in the original KD, which improves the recognition performance of the model. Additionally, SOKD is applicable to most CNNs for identify surface defect of hot-rolled strip. The experimental results on NEU-CLS dataset show that the SOKD outperforms state-of-the-art methods.

The quality of round billet is affected by the flow characteristics of molten steel during continuous casting. The application of nozzle swirling flow combined with electromagnetic stirrer (M-EMS) can increase the number of equiaxed crystal and alleviate macrosegregation, which has been demonstrated in our previous industrial test. However, flow field cannot be visually observed in industrial tests. In this paper, for the first time, the evolution of flow field and its influence on the macrosegregation and liquid level fluctuation under the action of coupled swirling flows were studied. Compared with that by using only mold stirring, the flow field was distributed more symmetrically in the upper part of mold and its impact depth decreased from 350 mm to 246 mm when the rotating speed of stirring propeller was 70 r/min. The centerline segregation level was reduced owing to the inward flow weakened by the outward nozzle swirling flow. Additionally, the tangential velocity at 1/2 radius near the surface was decreased from 0.589 m/s to 0.469 m/s, leading to the reduction of liquid level fluctuation. Consequently, both the internal quality and the surface quality can be improved by coupled swirling flows, provided that the rotating intensities of nozzle swirling flow and M-EMS are selected properly in the actual continuous casting production.

The decarburization kinetics according to the Ar-CO₂ ratio with a liquid Fe-1wt%C alloy was studied using a high-frequency induction furnace at 1873K. The carbon content in the liquid alloy decreased linearly with time, and as the CO₂ ratio increased, the decarburization rate of the liquid alloy increased. The main reaction turned out to be CO₂ + C = 2CO based on thermodynamic calculation. Comparing the amount of CO₂ gas blown into the liquid alloy and the carbon content in the liquid alloy, it was found that all CO₂ gas reacted with dissolved carbon when present as bubbles. A volume expansion model is proposed that takes into account the change in the partial pressure of gases due to the decarburization reaction and the resulting volume expansion of gases. Upon applying this model when S was low (50 ppm) and when S was high (0.1wt%), no differences were found in the three possible rate-controlling steps (gas phase mass transfer, dissociation&adsorption, and mixed control) when S was low, but Mixed control behavior was observed when S was high.

To investigate the influences of quasi-particles structure in the sintering bed on combustion behaviors and CO and NO emission, the non-isothermal combustion experiments and gas analysis were carried out by using coke breeze and sintering raw materials to prepare different types of quasi-particles. The results show that the four types of quasi-particles combustion processes were consistent with the unreacted nuclei model. The adhering layer had positive catalytic effects on coke breeze combustion and the reduction of NO by CO. Compared with S´_-0.25, the apparent activation energies of the C_71% and P_15%(2) combustion decreased by 1.85 kJ/mol and 27.34 kJ/mol, the CO emission reductions were 47.75% and 50.07%, and the NO emissions were reduced by 67.50% and 6.95%, respectively. Compared with S´_2~3, the apparent activation energies of the S_33%(2~3) decreased by 18.66 kJ/mol, and the emissions of CO and NO were decreased by 87.99% and 75.29%, respectively. Additionally, the structural changes of the four types of quasi-particles significantly affected the combustion and emission behaviors. The adhering fines of S-type, C-type and P-type had abundant porous structure, which provided active sites for the adsorption of CO and NO, promoted the reduction of NO by CO. In contrast, the emissions of S´-type gases were higher, and the emissions increased with increasing of size. Therefore, increasing the S-type content and reducing the S´-type content in the sintering bed will not only effectively improve the solid fuel combustion efficiency, ensure sufficient combustion zone temperature, but also greatly reduce emissions in the sintering flue gas.

Austenitic stainless steels such as SUS304 are widely used in various applications due to their excellent corrosion resistance; however, their low hardness and wear resistance limit their structural use. Plasma nitriding was applied using a Ti-Mo combination screen to simultaneously form a Ti-Mo composite nitride layer and a nitrogen diffusion layer in SUS304 stainless steel. The microstructure and mechanical properties of the plasma-nitrided SUS304 were evaluated. XRD analysis revealed peaks of δ-(Ti,Mo)N, which originated from the constituent elements of the screen, indicating the successful formation of a Ti-Mo-N composite nitride layer on the sample surface. The thickness of the Ti-Mo-N layer increased with higher gas pressure and nitrogen content in the gas mixture. The formation of the Ti-Mo-N layer on the nitrogen diffusion layer significantly enhanced the hardness and reduced the kinetic friction coefficient. The results suggest that this surface treatment method could be beneficial for improving the durability and lifespan of stainless steel components in demanding applications.

Viscosity of oxide melts is a fundamental physicochemical property that plays a critical role in important technological and natural processes like slag flow, slag/metal separation, volcano eruptions etc. Unfortunately, many oxides melt at extremely high temperatures and are highly corrosive in the liquid state, which makes experimental measurement of viscosity by conventional experimental techniques a difficult, expensive, and sometimes impossible task. In this case it might be helpful to use other methods to determine viscosity, such as modelling or simulation. In the present paper the shear viscosity coefficients of the liquid CaO, MgO, and Al₂O₃ have been simulated via the classical molecular dynamics and compared to the available viscosity data (e.g. experimental viscosities, other model predictions) collected and stored in a databank by one of the authors. Different viscosity calculation techniques (e.g. the Green-Kubo equation, the Einstein relation, and the non-equilibrium molecular dynamics methods) coupled with MD have been employed to ensure a more reliable viscosity calculation. It has been shown that the simulated viscosities of the CaO and MgO melts are close to those calculated by phenomenological viscosity models and represent a plausible estimation for viscosity of these unary systems. It has also been shown that the simulated viscosity of the Al₂O₃ melt is lower than the majority of the available experimental data. In general, it has been demonstrated that the molecular dynamics simulation could provide a reasonable estimation of viscosity, especially if no other viscosity data is available.

In the steelmaking process, most slags and fluxes often contain a solid phase, such as CaO. The suspension in which solid phases are suspended has higher viscosity than that of a pure matrix liquid. Therefore, it is expected that the viscosity of slag containing solid phases will increase. In this study, the terminal settling velocity of particles in a suspension has been measured. The suspensions consist of a silicone oil matrix and polyethylene beads, and the settling particles are bearing balls made of stainless steel. As a result of the higher viscosity of suspension, the terminal settling velocity of the bearing ball becomes slower than that in the pure silicone oil. It was clarified that the retardation of the terminal velocity and the increase in the drag coefficient depend only on the volume fraction of the solid phase (polyethylene beads) of the suspension, and they are independent of the size of the suspended beads and the viscosity of the matrix liquid. A correlation equation for predicting the drag coefficient of particles in a suspension was proposed.

The blast furnace ironmaking process relies heavily on fossil fuels, posing challenges to achieving carbon neutrality. New methods, like hydrogen reduction ironmaking, face limitations such as the need for high-grade iron ore and issues with DRI melting. To address these, biomass char has been explored as a carbon-neutral carburizing agent, yet practical application is difficult due to biomass supply limitations in East Asia. Thus, Carbon Capture and Utilization, CCU becomes essential. Examples include iACRES and carbon recycling blast furnaces, which recycle CO₂ for reducing agents but have limited scope.

Phase equilibria studies were undertaken on the FeO- Fe₂O₃ – MgO-SiO₂ and FeO -Fe₂O₃- MgO systems in air using an equilibration and quenching technique. Concentrations of Fe, Mg, Si in the coexisting phases were measured using electron probe X-ray microanalysis (EPMA) with a wavelength dispersive spectrometer (WDS) detector. The liquidus temperatures have been determined from 1400 °C to 1740 °C in primary phase fields of spinel, monoxide, olivine, pyroxene, tridymite, cristobalite and in two-liquids miscibility gap. Tielines between co-existing phases and the compositions of solid solutions have been determined. In the absence of a liquid phase which would facilitate mass transport, the subsolidus phase relations in the Fe₂O₃- MgO system were not studied directly. The measurements in the low-SiO₂ area of pseudo-ternary "Fe₂O₃" - MgO-SiO₂ system were used to derive phase equilibria of the "Fe₂O₃" -MgO pseudo-binary system with a special focus on the monoxide-spinel phase boundary. The present study is a part of the research program on the characterization of the MgO-containing refractory systems within the multicomponent Pb-Zn-Cu-Fe-Ca-Si-O-S-Al-Mg-Cr-Na-As-Sn-Sb-Bi-Ag-Au-Ni-Co system.

Slag foaming is a phenomenon caused by the generation of CO bubbles due to the reaction between iron oxide in slag and carbon in pig iron. The purpose of this study is to explore the controlling factors of slag foaming by observing the bubble formation behavior caused by the chemical reaction between iron oxide and Fe-C alloy in slag. 0.06 g of Fe-C alloy was charged to the bottom of the BN crucible, and 6.0 g of slag (SiO₂:CaO:Fe₂O₃ = 40:40:30) was charged on top of it. The crucible was placed in an infrared image heating furnace, and the temperature was rapidly raised to 1370°C at a rate of 1000°C/min in a N₂ stream, then held for a predetermined time and rapidly cooled. After rapidly cooling, the internal structure of the sample was observed using a high-resolution X-ray CT device. The spherical equivalent volume is calculated based on the number of bubbles observed and their equivalent circle diameter, and the relationship between the volume ratio of small bubbles in the slag volume and the distance from the bottom of the crucible is calculated, and the bubble density and volume ratio are calculated. It was suggested that the value tends to increase as the distance from the bottom of the crucible increases.

The compositional ranges of SFCA-I and other SFCA series and the phase equilibrium relationships were investigated in the iron-rich corner of the CaO-Fe₂O₃-Al₂O₃ system at 1240 ^°C in air using powder and single crystal XRD as well as EPMA. To obtain the desired composition, reagent-grade CaCO₃, Fe₂O₃, and Al₂O₃ powders were weighed, mixed, and equilibrated at 1240^oC in air. Each of the obtained samples was divided into two parts: one was pulverized into a powder and analyzed by XRD, and the other was subjected to microstructural observation and compositional analysis using EPMA. The crystalline structures of the SFCA series for some samples were analyzed by a single XRD. The results revealed that not only SFCA-I but also SFCA-II and SFCA have been found in the compositional area of this study; the Al/(Al+Ca+Fe) concentration ranges are 7.89–20.33 mol% for SFCA-I, 17.62–24.55 mol% for SFCA-II and 20.93–27.60 mol% or even higher for SFCA. The compositions of SFCA are on the line satisfying M₁₄O₂₀, while those of SFCA-I and SFCA-II deviate from the lines satisfying M₂₀O₂₈ and M₁₇O₂₄, respectively, and are closer to the line satisfying M₁₄O₂₀. Since the compositions were derived based on the assumption that all Fe irons are Fe³⁺, the apparent compositions of SFCA-I and SFCA-II deviate from M₂₀O₂₈ and M₁₇O₂₄, respectively, owing to the presence of trace amounts of Fe²⁺.

Foaming slag generated in the steelmaking process, especially in hot-metal pretreatment and electric arc furnaces, is a gas-liquid coexistent fluid with CO gas generated by the interfacial reaction between slag containing iron oxide and hot metal or carbonaceous materials. In addition, it is essential to understand the flow behavior of foaming slag during slag-tapping and the sedimentation behavior of iron particles, which affects iron yield, and to expand our knowledge of the viscosity of gas-liquid coexisting fluids for CFD modeling of these phenomena. In the present study, the apparent viscosity of a foaming slag was systematically investigated, which was generated by reacting CaO-SiO₂-Fe_xO slag with Fe-C alloy and varying the composition, gas phase ratio, and shear rate of the slag. By adding Fe-C alloy powder to the slag, bubbles were continuously generated in the molten slag, and foaming slag suitable for viscosity measurement could be prepared. It was found that the higher the amount of Fe-C alloy powder, the larger the gas phase ratio of the foaming slag due to an increase in the number of bubbles generated. The relative viscosity of the foaming slag was found to increase with the gas phase ratio. The higher the rotation speed, the smaller the relative viscosity of the foaming slag indicating shear-thinning characteristics. The relationship between shear rate and shear stress calculated from the viscosity of the foaming slag did not show general non-Newtonian fluid behavior.

Towards steelmaking processes which are compatible with the sustainable society, re-sulfurization reaction in hot metal pre-treatments needs to be suppressed as much as possible. To evaluate the effects of iron oxide on the sulfur distribution ratio between FeO-containing slag and hot metal, sulfide capacities and FeO activities were measured in CaO-SiO₂-FeO and CaO-Al₂O₃-FeO ternary liquid slags. Although the FeO activity and oxygen potential increased, the addition of FeO raised sulfide capacity drastically and resulted in an increase in the calculated value for distribution ratio of sulfur.

This study investigated the use of sustainable coal (lignite) that can simultaneously satisfy three requirements: [1] Environmental issues (CO₂), particularly Carbon dioxide Capture and Utilization (CCU) that reduces CO₂; [2] Resource issues, particularly Enhancement of dephosphorization function in the refining process; and [3] Enhancement of refining high-carbon steel. This study confirmed that use in the steel making process of lignite upgraded coal briquettes gives possibility to functionally differentiate the reaction site of decarbonization and dephosphorization and to reduce CO₂ emissions.

We measured the density of eight types of molten alkali silicate slag within the range of 1,673–1,823 K using the Archimedean double-bob method. The melt density of binary alkaline silicate glass linearly increased with a decrease in temperature. The temperature coefficient of the density ranged from -21.5 to -13.2 × 10^-5 g‧cm^-3‧K^-1, and its order corresponded to the order of the ionic radii of the alkali oxide components. We applied Doolittle's free volume theory by combining the reported values of melt viscosity with the measured densities and volume expansion coefficients of melts and glass solids to propose an equation for predicting melt density from slag composition and temperature. Melt densities in the range of 1,273–1,823 K were predicted and compared with experimental values.

The surface tension of the mold flux is important because it governs the interfacial phenomena between the mold and molten/solid steel. The maximum bubble pressure (MBP) method is often used to determine the surface tension of molten slags. However, for liquid samples with high viscosity, such as molten silicate, the MBP is overestimated. In this study, a simple relaxation function was applied to determine the MBP using the gas flow-rate as a parameter. Consequently, a static MBP was obtained, and the surface tension was reliably measured. The surface tension of the SiO₂-Na₂O-NaF melts were measured over a wide composition range using the developed method. When SiO₂-40 mol% Na₂O was added to NaF, the surface tension of the melts gradually increased with increase in SiO₂-Na₂O concentration. When the NaF in SiO₂-40 mol% NaF was replaced by Na₂O, the surface tension of the melts did not change significantly at the beginning of the addition. It was considered that F^- ion was exposed in the surface of melts instead of O^2- ion. This result is consistent with the discussion of the relative strength of the bonding force between the constituent particles. The increase in the surface tension upon further replacement of NaF with Na₂O was gradual, indicating that F^- was relatively exposed more than O^2- on the surface of the investigated melts.

The recovery rate of iron is reduced if iron particles suspended in the refining slag do not sediment. The sedimentation rate of particle iron in the foaming slag is slower than in the slag in the single-phase liquid. Iron particles are especially likely to remain in the foaming slag. To predict the sedimentation rate of iron particles in the slag, it is necessary to derive an accurate viscosity of the foaming slag. However, it is difficult to estimate an appropriate value because the state of gas-liquid multiphase fluid changes the condition with time. Its apparent viscosity varies depending on the measurement method because it is a non-Newtonian fluid. In this study, to understand the sedimentation behavior of iron particles in foaming slag, a gas-liquid multiphase fluid was generated by glycerin solution. Its apparent viscosity was estimated by the Stokes equation using the falling-ball method. The sedimentation rate of stainless steel, titanium, and glass balls with a diameter of 2 mm were measured in a glycerin aqueous solution gas-liquid fluid. The sedimentation rate was non-uniform because the gas-liquid fluid's state differed depending on the position. The apparent viscosity of the fluid increased with an increase in the gas phase ratio. The variation of apparent viscosity with the conditions of the falling-ball method was also discussed. Furthermore, a comparison was made between the present results and the apparent viscosity measured by the rotational technique.

The activities of components in Ca₂SiO₄-Ca₃P₂O₈ solid solutions have been reported by preceding studies as the basic thermodynamic data for phosphorus removal in the steelmaking process. Since the reported activities contained the uncertainties accumulated from thermodynamic data, this study aimed to reevaluate the experimental results in the preceding studies. Firstly, the equilibrium constant of the following reaction used to calculate the P₂O₅ activities was measured at 1573 K through a gas equilibrium method.

It is known that dephosphorization of molten iron is promoted by Ca₂SiO₄ precipitates in molten slag because they form a solid solution with Ca₃P₂O₈. Crystal structure of the Ca₂SiO₄ precipitate is important because it strongly affects phosphorus solubility. Although the α phase of the solid solution shows extremely high phosphorus solubility at high temperatures, its phase transition easily occurs to the α' phase that has low phosphorus solubility when iron oxide is incorporated in slag. Phase stability of Ca₂SiO₄ crystal strongly depends on the solubility of foreign components, which influence the ionic configuration. To explore the optimum composition for enhancing structural stability of the α phase, this study conducted a structure design of Ca₂SiO₄-based solid-solution crystal by first-principles calculation based on density functional theory. The effect of foreign component solubility on the α phase stability was evaluated by free energy change of solid-solution formation. It was found that Ca²⁺ substitution with Fe²⁺ in α-Ca₂SiO₄ crystal makes the structure unstable, whereas Ba²⁺ incorporation enhances stability. In the latter case, oxygen ion configuration becomes distorted and the structure is relaxed. High-temperature in-situ X-ray diffraction analysis was performed to observe precipitation of the Ca₂SiO₄-based solid solution in a molten slag and its phase transition with decreasing temperature. The α phase of the Ca₂SiO₄-based solid solution initially precipitated at 2073 K, while the α→α' phase transition and precipitation of the calcium ferrite phase occurred at temperatures lower than 1673 K. It was verified that the Ba-bearing Ca₂SiO₄ precipitates in slag contained significant phosphorus content.

This paper reviews studies on the prediction of ductile fracture during metal forming using an ellipsoidal void model and some other models proposed by the author and some relevant studies. Section 2 discusses the research on the theory of voids for predicting ductile fracture during metal forming. Section 3 summarizes the simulation method for predicting ductile fracture during metal forming using the ellipsoidal void model, and Section 4 summarizes the simulation result on the ductile fracture prediction during metal forming using the ellipsoidal void model. Section 5 shows the applicability of the ellipsoidal void model and the simulation result on the ductile fracture prediction during metal forming using some other models.

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

Fe-9 mass%Ni alloy is widely used as a cryogenic steel owing to its excellent low-temperature strength and toughness. However, Ni is an expensive element, with medium-Mn steel considered an inexpensive alternative. Considering the Fe-10%Mn-0.1%C alloy is brittle at low temperatures, the application of intercritical annealing with two-step hot rolling could lead to toughening. Herein, the effect of intercritical annealing on the toughness of a Fe-10%Mn-0.1%C alloy with elongated prior-austenite grains (PAGs) formed via a two-step hot-rolling process was investigated. Intercritical annealing was performed on the specimens with and without two-step hot rolling. For both specimens, intercritical annealing resulted in softening of α'-martensite and an increase in the amount of retained austenite. In the specimen not subjected to the two-step hot rolling process, the fracture morphology transitioned from ductile to intergranular with a decrease in the temperature. Intercritical annealing improved the toughness when ductile fracture occurred. In the case of intergranular fracture, the effect of intercritical annealing on the toughness was negligible. In the two-step hot-rolled specimen with elongated PAGs, the fracture morphology transitioned from ductile to separation fracture with ductile fracture, and intercritical annealing improved the toughness at all temperature ranges. The improvement in toughness during separation fracture is attributed to the expansion of the plastic zone owing to ductile crack progression and the formation of sub-cracks, which promote the strain-induced transformation of retained austenite and ε-martensite.

From the viewpoint of expanding the allowable P limit, the effect of warm tempforming on delayed fracture resistance was evaluated for 0.09% P-doped 0.4%C–1%Cr–0.7%Mn–0.2%Mo steel (mass%). The P-doped steel was warm tempformed at 500 °C with a caliber-rolling reduction of 78% and annealed at 550 °C for 1 h. This thermomechanical treatment created an ultrafine elongated grain structure with a strong <110>// rolling direction fiber texture, in which P definitely cosegregated with Mn and Mo at grain boundaries. The slow-strain-rate-test and immersion test demonstrated that warm tempforming markedly enhanced the delayed fracture resistance of the P-doped steel at a tensile strength of 1100 MPa level, in contrast to conventional quenching and tempering treatment.

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.

The interfacial tension between the liquid steel and molten slag is one of the key properties to control the entrapment of mold flux in molten steel in the continuous casting process. A dynamic change of the interfacial tension is observed when deoxidized iron and silicate slag are in contact, which can be explained by the oxygen absorption and desorption at the iron/slag interface. However, the dynamic change of the interfacial tension is influenced by other surfactant components of the molten iron and slag. Fluoride ions are fundamental component of mold flux, and recognized as the surface active component of molten slag. The effect of fluoride ions in slag on the interfacial tension has not been critically evaluated. Here, the effect of fluoride ions in slag on the interfacial tension between molten iron and molten silicate slag was evaluated at 1823 K, where the fluoride-containing slag compositions were designed to exhibit the same SiO₂ activity and slag viscosity as those of the fluoride-free slag. Compared with the case of molten iron and fluoride-free slag, the interfacial tension between the molten iron and fluoride-containing slag was initially lower. Except the effect of oxygen adsorption, fluoride ion was considered to directly decrease the interfacial tension. However, as the fluoride content in slag was higher, the interfacial tension tended to show the higher value at the final state. This behavior was attributed mainly to fluoride vaporization as SiF₄, which reduce the SiO₂ activity in slag and thus equivalent oxygen content at the iron/slag interface.

A novel integrated constitutive equation of the flow curve for Ti–6Al–4V alloys is proposed by incorporating the effects of phase fraction in the hot-forging temperature range. The flow curve was obtained using hot-compression tests in the temperature range of 750–1050 °C and strain rate range of 1–25 s^-1. The effects of friction and deformation heat generated during compression were corrected using the inverse analysis method to identify the ideal uniaxial flow curve. The obtained stress parameters were satisfactorily regressed using the rule of mixtures on the α and β phases considering changes in the phase fraction. The integrated flow curve equation incorporating the rule of mixtures of the two phases effectively expressed the flow curve throughout the investigated temperature range. The internal microstructural observation showed that the continuous dynamic recrystallization of the α phase is dominant in the α+β two-phase region, while the deformation of the β phase becomes dominant just below the β transus. The constitutive equation presented here is in good agreement with the temperature dependence of the microstructure.